Cambridge A Level Mathematics - Further 9231 — 2022 May/June Paper 1 · Variant 3

This document has 20 pages. Any blank pages are indicated. [Turn over Cambridge International AS & A Level * 2 2 1 3 4 5 4 5 7 9 * DC (CE) 214265/1 © UCLES 2022 FURTHER MATHEMATICS 9231/13 Paper 1 Further Pure Mathematics 1 May/June 2022 2 hours You must answer on the question paper. You will need: List of formulae (MF19) INSTRUCTIONS ● Answer all questions. ● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. ● Write your name, centre number and candidate number in the boxes at the top of the page. ● Write your answer to each question in the space provided. ● Do not use an erasable pen or correction fluid. ● Do not write on any bar codes. ● If additional space is needed, you should use the lined page at the end of this booklet; the question number or numbers must be clearly shown. ● You should use a calculator where appropriate. ● You must show all necessary working clearly; no marks will be given for unsupported answers from a calculator. ● Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place for angles in degrees, unless a different level of accuracy is specified in the question. INFORMATION ● The total mark for this paper is 75. ● The number of marks for each question or part question is shown in brackets [ ].

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3 9231/13/M/J/22 © UCLES 2022 [Turn over 1 (a) Sketch the curve with equation y x x 1 1 = - + . [2] (b) Sketch the curve with equation y x x 1 1 = - + and find the set of values of x for which x x 1 1 2 1 - + - . [4] … … … …

4 9231/13/M/J/22 © UCLES 2022 2 The cubic equation x x x 5 10 2 0 3 2 + + - = has roots a, b, c. (a) Find the value of 2 2 2 a b c + + . [3] … … … … … … … … … … … … … … … … … … … … … … … … … …

5 9231/13/M/J/22 © UCLES 2022 [Turn over (b) Show that the matrix 1 1 1 a b a c b c f p is singular. [4] … … … … … … … … … … … … … … … … … … … … … … … … … …

6 9231/13/M/J/22 © UCLES 2022 3 A curve C has equation y x ax x 1 1 2 = - + - , where a is a positive constant. (a) Find the equations of the asymptotes of C. [3] … … … … … … … … … … … … (b) Show that there is no point on C for which y a 1 1 4 1 1 + . [4] … … … … … … … … … … … …

7 9231/13/M/J/22 © UCLES 2022 [Turn over … … … … … … … … … … (c) Sketch C. You do not need to find the coordinates of the intersections with the axes. [3]

8 9231/13/M/J/22 © UCLES 2022 4 Let ) u 2 1 e (e e r rx x x 2 = - + . (a) Using the method of differences, or otherwise, find ur r n 1 =/ in terms of n and x. [3] … … … … … … … … … … … … … (b) Deduce the set of non-zero values of x for which the infinite series u u u 1 2 3 f + + + is convergent and give the sum to infinity when this exists. [3] … … … … … … … … … …

9 9231/13/M/J/22 © UCLES 2022 [Turn over … … … … … … … … … … (c) Using a standard result from the list of formulae (MF19), find lnur r n 1 =/ in terms of n and x. [3] … … … … … … … … … … … … … … … … …

10 9231/13/M/J/22 © UCLES 2022 5 Let a A 1 0 1 = e o, where a is a positive constant. (a) State the type of the geometrical transformation in the x–y plane represented by A. [1] … … (b) Prove by mathematical induction that, for all positive integers n, na A 1 0 1 n = e o. [5] … … … … … … … … … … … … … … … … … … … … … …

11 9231/13/M/J/22 © UCLES 2022 [Turn over Let b a b a B 1 1 = - - e o, where b is a positive constant. (c) Find the equations of the invariant lines, through the origin, of the transformation in the x–y plane represented by A B n . [6] … … … … … … … … … … … … … … … … … … … … … … … … …

12 9231/13/M/J/22 © UCLES 2022 6 The curve C has Cartesian equation x xy y a 2 2 + + = , where a is a positive constant. (a) Show that the polar equation of C is sin r a 2 2 2 2 i = + . [3] … … … … … … … … … … … … (b) Sketch the part of C for r 0 4 1 G G i . [2]

13 9231/13/M/J/22 © UCLES 2022 [Turn over The region R is enclosed by this part of C, the initial line and the half-line r 4 1 i = . (c) It is given that sin2i may be expressed as tan tan 1 2 2i i + . Use this result to show that the area of R is tan tan tan a 1 1 d r 2 1 2 2 0 4 1 i i i i + + + y and use the substitution tan t i = to find the exact value of this area. [8] … … … … … … … … … … … … … … … … … … … … … …

14 9231/13/M/J/22 © UCLES 2022 7 The position vectors of the points A, B, C, D are i j k 7 4 + - , i j 11 3 + , i j k 2 6 3 + + , i j k 2 7 m + + respectively. (a) Given that the shortest distance between the line AB and the line CD is 3, show that 5 4 0 2 m m - + = . [7] … … … … … … … … … … … … … … … … … … … … … … … …

15 9231/13/M/J/22 © UCLES 2022 [Turn over Let 1 P be the plane ABD when 1 m = . Let 2 P be the plane ABD when 4 m = . (b) (i) Write down an equation of 1 P , giving your answer in the form s t r a b c = + + . [2] … … … … (ii) Find an equation of 2 P , giving your answer in the form ax by cz d + + = . [4] … … … … … … … … … … … … … … … … … … … …

16 9231/13/M/J/22 © UCLES 2022 (c) Find the acute angle between 1 P and 2 P . [5] … … … … … … … … … … … … … … … … … … … … … … … … … … …

17 9231/13/M/J/22 © UCLES 2022 Additional page If you use the following page to complete the answer to any question, the question number must be clearly shown. … … … … … … … … … … … … … … … … … … … … … … … … … …

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20 9231/13/M/J/22 © UCLES 2022 BLANK PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Cambridge Assessment International Education is part of Cambridge Assessment. Cambridge Assessment is the brand name of the University of Cambridge Local Examinations Syndicate (UCLES), which is a department of the University of Cambridge.

This document consists of 17 printed pages. © UCLES 2022 [Turn over Cambridge International AS & A Level FURTHER MATHEMATICS 9231/13 Paper 1 Further Pure Mathematics 1 May/June 2022 MARK SCHEME Maximum Mark: 75 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge International will not enter into discussions about these mark schemes. Cambridge International is publishing the mark schemes for the May/June 2022 series for most Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components.

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 2 of 17 Generic Marking Principles These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside the specific content of the mark scheme or generic level descriptors for a question. Each question paper and mark scheme will also comply with these marking principles. GENERIC MARKING PRINCIPLE 1: Marks must be awarded in line with:  the specific content of the mark scheme or the generic level descriptors for the question  the specific skills defined in the mark scheme or in the generic level descriptors for the question  the standard of response required by a candidate as exemplified by the standardisation scripts. GENERIC MARKING PRINCIPLE 2: Marks awarded are always whole marks (not half marks, or other fractions). GENERIC MARKING PRINCIPLE 3: Marks must be awarded positively:  marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond the scope of the syllabus and mark scheme, referring to your Team Leader as appropriate  marks are awarded when candidates clearly demonstrate what they know and can do  marks are not deducted for errors  marks are not deducted for omissions  answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the question as indicated by the mark scheme. The meaning, however, should be unambiguous. GENERIC MARKING PRINCIPLE 4: Rules must be applied consistently, e.g. in situations where candidates have not followed instructions or in the application of generic level descriptors. GENERIC MARKING PRINCIPLE 5: Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may be limited according to the quality of the candidate responses seen). GENERIC MARKING PRINCIPLE 6: Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thresholds or grade descriptors in mind.

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 3 of 17 Mathematics Specific Marking Principles 1 Unless a particular method has been specified in the question, full marks may be awarded for any correct method. However, if a calculation is required then no marks will be awarded for a scale drawing. 2 Unless specified in the question, answers may be given as fractions, decimals or in standard form. Ignore superfluous zeros, provided that the degree of accuracy is not affected. 3 Allow alternative conventions for notation if used consistently throughout the paper, e.g. commas being used as decimal points. 4 Unless otherwise indicated, marks once gained cannot subsequently be lost, e.g. wrong working following a correct form of answer is ignored (isw). 5 Where a candidate has misread a number in the question and used that value consistently throughout, provided that number does not alter the difficulty or the method required, award all marks earned and deduct just 1 mark for the misread. 6 Recovery within working is allowed, e.g. a notation error in the working where the following line of working makes the candidate’s intent clear.

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 4 of 17 Mark Scheme Notes The following notes are intended to aid interpretation of mark schemes in general, but individual mark schemes may include marks awarded for specific reasons outside the scope of these notes. Types of mark M Method mark, awarded for a valid method applied to the problem. Method marks are not lost for numerical errors, algebraic slips or errors in units. However, it is not usually sufficient for a candidate just to indicate an intention of using some method or just to quote a formula; the formula or idea must be applied to the specific problem in hand, e.g. by substituting the relevant quantities into the formula. Correct application of a formula without the formula being quoted obviously earns the M mark and in some cases an M mark can be implied from a correct answer. A Accuracy mark, awarded for a correct answer or intermediate step correctly obtained. Accuracy marks cannot be given unless the associated method mark is earned (or implied). B Mark for a correct result or statement independent of method marks. DM or DB When a part of a question has two or more ‘method’ steps, the M marks are generally independent unless the scheme specifically says otherwise; and similarly, when there are several B marks allocated. The notation DM or DB is used to indicate that a particular M or B mark is dependent on an earlier M or B (asterisked) mark in the scheme. When two or more steps are run together by the candidate, the earlier marks are implied and full credit is given. FT Implies that the A or B mark indicated is allowed for work correctly following on from previously incorrect results. Otherwise, A or B marks are given for correct work only.  A or B marks are given for correct work only (not for results obtained from incorrect working) unless follow through is allowed (see abbreviation FT above).  For a numerical answer, allow the A or B mark if the answer is correct to 3 significant figures or would be correct to 3 significant figures if rounded (1 decimal place for angles in degrees).  The total number of marks available for each question is shown at the bottom of the Marks column.  Wrong or missing units in an answer should not result in loss of marks unless the guidance indicates otherwise.  Square brackets [ ] around text or numbers show extra information not needed for the mark to be awarded.

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 5 of 17 Abbreviations AEF/OE Any Equivalent Form (of answer is equally acceptable) / Or Equivalent AG Answer Given on the question paper (so extra checking is needed to ensure that the detailed working leading to the result is valid) CAO Correct Answer Only (emphasising that no ‘follow through’ from a previous error is allowed) CWO Correct Working Only ISW Ignore Subsequent Working SOI Seen Or Implied SC Special Case (detailing the mark to be given for a specific wrong solution, or a case where some standard marking practice is to be varied in the light of a particular circumstance) WWW Without Wrong Working AWRT Answer Which Rounds To

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 6 of 17 Question Answer Marks Guidance 1(a) B1 Axes and asymptotes. B1 Branches correct. 2 x y

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 7 of 17 Question Answer Marks Guidance 1(b) B1 FT FT from sketch in part (a), symmetrical about 0.  x B1 Correct shape at 0  x (reflection not turning point). 1 2 1    x x 1 3 leading to x  M1 Finds critical point(s). 1 3 1 ,   x 1 3 1   x A1 4

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 8 of 17 Question Answer Marks Guidance 2(a) 10       B1 SOI 2 2 2 2 5 20 5         M1 A1 Uses     2 2 2 2 2 .                  Alternative method for question 2(a) Put 2  y x and form cubic not involving x M1 A1 2 2 ( 10) 25 20 4     y y y y (need not be simplified). 3 2 5 120 4 0     y y y   2 2 2 ( 5) 5        A1 3 2(b) 2 2 2 1 1 1 1 2 1 1 1 1                             M1 A1 Finds determinant. 2 2 2 0 1 1 2 2 5 2( )            M1 A1 Substitutes and uses 2  4

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 9 of 17 Question Answer Marks Guidance 3(a) 1  x B1 States vertical asymptote.   ) 1 1 1 ( 1 1            x ax a a y a ax a x x M1 Finds oblique asymptote. 1    y ax a A1 3

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 10 of 17 Question Answer Marks Guidance 3(b) 2 2 1 leading to ( 1) ( 1) 0 ax x yx y ax y x y         M1 A1 Forms a three term quadratic in x.   2 1 4 ( 1) 0     y a y M1 Correct inequality using discriminant. 1 1 4   y a A1 AG Clear method to reach given answer eg ( 1)( 1 4 ) 0    y y a Alternative method for question 3(b) 2 2 1 leading to ( 1) ( 1) 0 ax x yx y ax y x y         M1 A1 Forms three term quadratic in x.   2 1 4 ( 1) 0     y a y M1 Correct inequality using discriminant. Must be clear looking for where values of y exist. 1 1 4   y a A1 AG Clear method to reach given answer eg ( 1)( 1 4 ) 0   y y a  Second alternative method for question 3(b) 2 2 d ( 1)(2 1) ( 1) 0 d ( 1) y x ax ax x x x         M1 0  x or 2  x A1 Proves (0, 1) is local maximum and (2,4 1)  a is local minimum. M1 Either 2 2 d d y x or gradient either side Reference to position of asymptote or two distinct branches to justify 1 1 4   y a A1 AG 4

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 11 of 17 Question Answer Marks Guidance 3(c) B1 FT Asymptotes identified. FT from part 3a. B1 Two branches in correct position relative to correct asymptotes and of correct shape. Good asymptotic behaviour. B1 Lower branch in all four quadrants from correct asymptotes. 3

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 12 of 17 Question Answer Marks Guidance 4(a)   1 2 3 2 e e 2e 1 e 2e e        rx x x n x r x x 4 3 2 e 2e e    x x x 5 4 3 e 2e e    x x x  ( 1) ( 1) e 2e e      n x nx n x ( 2) ( 1) e 2e e      n x n x nx M1 A1 Shows enough complete terms to make pattern of cancelling clear GP method.     1 2 2 (e ) 1 e 2e 1 e e 2e 1 e e 1          x x x r x n x r x x n x 2 ( 1) ( 2) e e e e       x x n x n x A1 OE ( 1)( 1)   x x nx e e e 3 4(b) 0  x B1 Accept 0. x  2 1 2 3 t e 0 lead s ing a e e o x x nx n u u u         M1 A1 Must see ] e 0[as    nx n agreeing with their set of x 3 4(c) 2 1 1 ln ( ln(e 1) )        x r r n n r u rx M1* Uses laws of logarithms correctly. 1 ln n r ru  2 1 2 ( 1) ln(e 1)     x xn n n dM1 A1 Applies 1 2 1 ( 1).     n r r n n AEF for 2 ln(e 1)   x n 3

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 13 of 17 Question Answer Marks Guidance 5(a) A shear in the x-direction. B1 Accept ‘shear’. 1 5(b) 1 0 1       a A so true when 1.  n B1 States base case. Assume that it is true for  n k , so 1 0 1       k ka A . B1 States inductive hypothesis. Then 1 1 1 1 1 ( 1) 0 1 0 1 0 1 0 1                            k ka a a ak k a A M1 A1 Multiplies k A with A . If it is true for [ 1  n and]  n k then it is also true for 1   n k . Hence, [by induction,] true for all positive integers. A1 Everything correct and states conclusion. 5 5(c) 1 1 1 1 1 0 1                      a a a n a b b b n b n na A B M1 A1 Uses formula given in part (b). 1 1 1 ( )( ) ( )                     a a a b n x y b n b n x x y y B1 Transforms       x y by multiplying matrices to find       X Y . 1 (1 ) ( )(1 )     a m m b n m M1 Uses  y mx and  Y mX y x  A1 1 ( )  a b n y x A1 6

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 14 of 17 Question Answer Marks Guidance 6(a) cos  x r sin  y r 2 2 2   x y r B1 SOI     1 2 2 2 co 1 sin 1 sin 2 s        r r a M1 Eliminates both x and y and uses the double angle formula. 2 2 2 sin 2   a r A1 AG 3 6(b) B1 Polar graph with curve in correct domain. Graph needs gradient 0  and 0  r for all  in the domain. B1 r strictly decreasing such that r at π 4  is greater than half at 0 r  . Concave graph. Gradient at π 0 and 4  must not be vertical or horizontal, respectively. 2

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 15 of 17 Question Answer Marks Guidance 6(c)   1 4 1 4 π 2 1 π 2 2 0 0 2 1 tan 2 1 tan 2tan R r d a d              B1 AG 2 d leading to s c tan e d t t     M1 Applies given substitution. 2 2 d sec 1 d    t t M1 Applies 2 2 sec 1 tan    0 2 1 1 2 1 d 1    R a t t t A1 4 2 2 3 1 2 1 ( )    t t t B1 Completes the square.   1 1 1 1 2 1 2 3 3 3 3 1 0 0 2 4 1 2 1 d tan ( )            R a t a t t M1 A1 Applies formula. π 6 3 a A1 8

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 16 of 17 Question Answer Marks Guidance 7(a) ( ) 4 3         AB CD i j k j k B1 Finds direction vectors of the two lines. 2 4 1 1 12 4 0 1 3 4                   i j k M1 A1 Finds common perpendicular. This may also be done by setting up simultaneous equations and solving them. 2 2 5 1 2 12 4 (4 16 4 2 ( 2) 1 4 2)                            M1 A1 Uses formula for perpendicular distance.   2 2 2 4 30 3 3 9( ) 9 17 100 17 10 1 1 1 6 64 00                M1 Sets equal to 3 and forms in quadratic in . 2 2 64 0 leading to 4 0 16 80 5           A1 AG 7 7(b)(i)     7 4 4 5 3 2          t s r i j k i j k i j k M1 A1 OE M1 for using a correct point and attempting to find relevant direction vectors. 2 7(b)(ii) 8 4 1 1 25 5 3 5 7               i j k M1 A1 Finds normal to the plane 2 . 8(7) 25(4) 7( 1) leading to 8 25 7 163 x y z         M1 A1 Substitutes point. 4

9231/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2022 © UCLES 2022 Page 17 of 17 Question Answer Marks Guidance 7(c) 5 4 1 1 13 5 3 2 7               i j k M1 A1 Finds normal to the plane 1.  414 243 738 cos leading to cos 243 738 5 8 13 25 7 7                         M1 A1 Uses dot product of normal vectors. cos 0.9776176...  12.1 A1 Mark final answer. Accept 0.212c 5