General Certificate of Education Advanced Level Examination January 2010

Transcription

1 General Certificate of Education Advanced Level Examination January 010 Mathematics MFP4 Unit Further Pure 4 Monday January am to 10.0 am For this paper you must have: a 1-page answer book the blue AQA booklet of formulae and statistical tables. You may use a graphics calculator. Time allowed 1 hour 0 minutes Instructions Use black ink or black ball-point pen. Pencil should only be used for drawing. Write the information required on the front of your answer book. The Examining Body for this paper is AQA. The Paper Reference is MFP4. Answer all questions. Show all necessary working; otherwise marks for method may be lost. Information The marks for questions are shown in brackets. The maximum mark for this paper is 7. Advice Unless stated otherwise, you may quote formulae, without proof, from the booklet. P199/Jan10/MFP4 6/6/6/ MFP4

2 Answer all questions. 1 The matrix M represents the plane transformation T. Write down the value of det M in each of the following cases: (a) (b) (c) T is a rotation; T is a reflection; T is a shear; (d) T is an enlargement with scale factor. (4 marks) The diagram shows the parallelepiped ABCDEFGH. H G E D F C A B The position vectors of A, B, C, D and E are, respectively, 1 7 a ¼ 4, b ¼ 4, c ¼ 4 10, d ¼ 4 10 and e ¼ (a) Show that the area of ABCD is 7. (4 marks) (b) Find the volume of ABCDEFGH. ( marks) (c) Deduce the distance between the planes ABCD and EFGH. ( marks) 4 10 P199/Jan10/MFP4

3 The matrices A and B are defined in terms of a real parameter t by 1 1 A ¼ 4 t 4 and B ¼ t (a) Find, in terms of t, the matrix AB and deduce that there exists a value of t such that AB is a scalar multiple of the identity matrix I. ( marks) (b) For this value of t, deduce A 1. ( marks) 4 (a) Determine the two values of k for which the system of equations x y þ kz ¼ ðk þ 1Þx þ y ¼ k x þ y þðk 1Þz ¼ does not have a unique solution. (4 marks) (b) Show that this system of equations is consistent for one of these values of k, but is inconsistent for the other. (You are not required to find any solutions to this system of equations.) (8 marks) The plane transformations T A and T B are represented by the matrices A and B respectively, 1 where A ¼ and B ¼. 1 (a) Find the equation of the line which is the image of y ¼ x þ 1 under T A. ( marks) (b) The rectangle PQRS, with area 4. cm, is mapped onto the parallelogram P 0 Q 0 R 0 S 0 under T B. Determine the area of P 0 Q 0 R 0 S 0. ( marks) (c) The transformation T C is the composition T B followed by T A By finding the matrix which represents T C, give a full geometrical description of T C. ( marks) Turn over for the next question P199/Jan10/MFP4 Turn over s

4 4 6 (a) Find the value of p for which the planes with equations r p þ 1 ¼ 4 and r. 4 p ¼ 7 1 (i) are perpendicular; ( marks) (ii) are parallel. ( marks) (b) In the case when p ¼ 4: (i) write down a cartesian equation for each plane; ( marks) (ii) find, in the form r ¼ a þ ld, an equation for l, the line of intersection of the planes. (6 marks) (c) Determine a vector equation, in the form r ¼ u þ bv þ gw, for the plane which contains l and which passes through the point ð0, 7, 0Þ. ( marks) 16 q 7 7 (a) It is given that D ¼ 1 1 q q. (i) By using row operations on the first two rows of D, show that ð4 qþ is a factor of D. ( marks) (b) (ii) Express D as the product of three linear factors. (4 marks) It is given that M ¼ 4 (i) Verify that is an eigenvector of M and state its corresponding eigenvalue. 7 ( marks) (ii) For each of the other two eigenvalues of M, find a corresponding eigenvector. (7 marks) (c) The transformation T has matrix M. Write down cartesian equations for any one of the invariant lines of T. ( marks) END OF QUESTIONS Copyright Ó 010 AQA and its licensors. All rights reserved. P199/Jan10/MFP4

5 MFP4 - AQA GCE Mark Scheme 010 January series Key to mark scheme and abbreviations used in marking M m or dm A B E mark is for method mark is dependent on one or more M marks and is for method mark is dependent on M or m marks and is for accuracy mark is independent of M or m marks and is for method and accuracy mark is for explanation or ft or F follow through from previous incorrect result MC mis-copy CAO correct answer only MR mis-read CSO correct solution only RA required accuracy AWFW anything which falls within FW further work AWRT anything which rounds to ISW ignore subsequent work ACF any correct form FIW from incorrect work AG answer given BOD given benefit of doubt SC special case WR work replaced by candidate OE or equivalent FB formulae book A,1 or 1 (or 0) accuracy marks NOS not on scheme x EE deduct x marks for each error G graph NMS no method shown c candidate PI possibly implied sf significant figure(s) SCA substantially correct approach dp decimal place(s) No Method Shown Where the question specifically requires a particular method to be used, we must usually see evidence of use of this method for any marks to be awarded. However, there are situations in some units where part marks would be appropriate, particularly when similar techniques are involved. Your Principal Examiner will alert you to these and details will be provided on the mark scheme. Where the answer can be reasonably obtained without showing working and it is very unlikely that the correct answer can be obtained by using an incorrect method, we must award full marks. However, the obvious penalty to candidates showing no working is that incorrect answers, however close, earn no marks. Where a question asks the candidate to state or write down a result, no method need be shown for full marks. Where the permitted calculator has functions which reasonably allow the solution of the question directly, the correct answer without working earns full marks, unless it is given to less than the degree of accuracy accepted in the mark scheme, when it gains no marks. Otherwise we require evidence of a correct method for any marks to be awarded.

6 MFP4 - AQA GCE Mark Scheme 010 January series Q Solution Marks Total Comments 1(a) 1 B1 (b) 1 (c) 1 B1 B1 (d) 9 B1 4 Total 4 (a) 4 8 AB AD = = 1 8 Attempt at vector product of any two suitable vectors Magnitude of this attempted = 7 4 ft on minus signs only AG (b) 1 AB AD AE = = Attempt at scalar triple product (or ) on any suitable vectors ft (c) Distance = (b) / 7 = 6 ft; must be deduced Total 8 (a) 4t 0 0 Decent attempt at AB 98 t 4t4 t14 correct 8 4t 0 4 all correct t = 7 Allow this ft if only 1 or elements of AB incorrect AB = 4I Must be from AB completely correct (b) A 1 = B1 B1 ft 1/det if related to B CAO; must be deduced NB 1 B scores B1 only 4 Total 7

7 MFP4 - AQA GCE Mark Scheme 010 January series MFP4 (cont) Q Solution Marks Total Comments 4(a) 1 k k = k Attempt at det. of coefft. mtx. k Correct 1 k 1 k =, 1 4 Setting det. = 0 and solving for k (b) k = = x y+ z 8 = x+ y = x + y + z B1 ft Eliminating one variable twice 8x + 9y = / 1y 8z = 1 / x + z = 11 ; Correct eqn. once; twice k = 1 = x yz 1 = y = x + y z x z = 1 / x z = 10 OR y = 1 and y = 7 found (a) 1 x x1 = x+ 1 x+ / x z = 11 B1 8 Total 1 ft Eliminating one variable twice Inconsistency correctly shown x Use of x + 1 ; either term correct giving y = 1 x CSO (b) Finding det(b) (= 1) and mult g. by 4. = 4. cm ft (c) 1 1 = This is a shear parallel to the x-axis AB attempted mapping (eg) (1, 1) to (, 1) Any point not on Ox and its image Total 10

8 MFP4 - AQA GCE Mark Scheme 010 January series MFP4 (cont) Q Solution Marks Total Comments 6(a)(i) 6 4p + 1 p = 0 1 Equating dot product to zero 4p + 6 p = 0 Solving a linear eqn. in t p = CAO (ii) 6 4p + 1 m p = 1 m =, p = 1, 6 4p + 1 ALT p = 0 1 p = 1 1 p 8p 4 18p 9 () () (b)(i) 6x y + z = 4, 17x + y + z = 7 B1,B1 (ii) eg. 1: 7[4x + y = 8] Eliminating one variable; correct x+ y = =λ 1 4 Parametrisation attempt Substituting back to find rd variable m1 z = 9λ r = 8, 1 or 0 + λ 4 B1 6 ft (any pt. on l) OR method for finding the d.v. 4 9 (M) Method for finding any pt. on l () Putting them together as a line eqn. (B1) ft (c) r = a + u d 1 + v d where a is an pt. on plane ft their previous a; or (0, 7, 0) d 1 = any d.v. ft their previous d.v. 0 d = 7 any a in plane 0 ft if is clear where it has come from Total 16

9 MFP4 - AQA GCE Mark Scheme 010 January series MFP4 (cont) Q Solution Marks Total Comments 7(a)(i) R 1 = R 1 + R or R = R + R 1 leading to R 1/ = (4 q 4 q 0) (ii) Δ= (4 q) 1 1q q = (4 q) q11 1q q = (4 q)( q11) 1 1q q By C 1 = C 1 C (eg) nd linear factor correct = (4 q)(q 11) Full attempt at rd factor = (4 q)(q 11)(q 10) 4 (b)(i) = = 4 so that λ = 4 7 (ii) λ = 10, 11 noted or used B1 ft λ = 10 0 = 6x + y+ 7 z 0 = 1x 11y7z 0 = 6x+ 6 y B1 Using y = x to get z x / y Eigenvector ( 7, 7, 1) Any non-zero multiple will do λ = 11 0 = x + y+ 7 z 0 = 1x 1y7z 0 = 6x+ 6 yz B1 Either y = x or z = 0 Eigenvector (1, 1, 0) 7 Any non-zero multiple will do (c) x y z x y = =, = = z Any line eqns. or x = y, z = 0 any one ft correct Total 18 TOTAL 7

10 AQA Further pure 4 Jan 010 Answers Question 1: 1) The moduls of the determinant of the matrix is the area scale factor of the transformation. a) Rotation : det( M) = 1 b) Reflection: det( M)= 1 c)shear: det( M) = 1 d) Enlargement: det( M) = = 9 Exam report This was a straightforward starter to the paper, yet one that still required a bit of thought; especially with parts (b) and (d), where, respectively, the minus sign and the extra factor of were often overlooked. Question : a) Area ABCD = AB AD 4 8 AB = b a= 0 and AD = d a= 7 i j k AB AD = 4 0 = i j+ k AB AD = 1i+ 1j+ 8k Area ABCD = AB AD = (1) + (1) + (8) = 7 b)the volume of the parallelepiped is V= AE. AB AD ( ) 1 AE = e a= 1 and AB AD = AE. ( AB AD) = 1. 1 = = 6 8 Volume = c)the distance between the two planes is the height of the parallelepiped, h. Volume of parallelepiped = Area of the base height = 7 h = so h = 6 Exam report Apart from a small minority of candidates who worked with the position vectors of A, B etc rather than the vectors AB, AD etc, this was usually found quite straightforward at least up until part (c), when the significance of the word deduce was almost universally ignored. Its original intention was to spare candidates from lengthy amounts of working, and point them in the direction of the obvious method, reinforced by the inclusion of a diagram. Remarkably few candidates spotted that the required distance was simply part (b) s answer divided by part (a) s, which was a shame for those who went ahead with other methods, as they received no credit. That said, almost no-one who tried one of these other methods obtained the right answer anyway.

11 Question : A= t 4 and t 4 B= t t 0 0 AB = 0 t t 16 t 1 98 t 4t 4 t = 4 4t t 0 4 If AB = ki then k must be 4. Is there a value of t for which t = t = t = t = and t = 4 4, 4 4 4, 14 0, ? When t = 7 all the equations are satisfied. b) If AB=4I then A AB = 4A B A A B = 4 I = = Exam report The matrix multiplication was generally handled very well, apart from a small but noticeable number of candidates who insisted on attempting BA despite the question. The only other obstacle to a completely correct part (a) was found amongst those candidates who had the odd one or two incorrect elements, which they had failed to notice and correct due to a lack of a check, meaning that t = 7 did not actually give 4I consistently for their AB. As with question, the word deduce in part (b) was almost totally ignored, and alternative methods for finding an inverse, often taking up lots of time, received no credit. Question 4: a)the system of equations is equivalent to the matrix equation: 1 k x k 1 0 y k + = 1 k1 z The system does not have a unique solution means that the determinant of the matrix is 0 1 k k = 0 this gives ( k 1) + ( k + 1)( k 1) + k( k + 1 6) = 0 1 k 1 k + k + k k = 0 k k 0 = (k )( k+ 1) = 0 k = or k = 1 b) for k =1, the system becomes xy z = l1 xy z = y = 1 l after combining y =1 x+ y z = l y = 7 ( l1+ l) The system is inconsistent for k = 1 for k =, the system becomes x y + z = l1 x 6y+ z = 1 L1 8 x+ y = l Multiplying by 8x+ 9y = L 6x+ y+ z = 9 L x+ y+ z = l x 6y+ z = 1 ' Eliminating zby combining the equations: 8x+ 9y = L ' ' 4x+ 7y = 1 L = L L1( = L) The system is consistent. Exam report This question was surprisingly well attempted, as the algebra that goes with the systems of equations work is usually found tough enough to guarantee lots of mistakes. Almost all candidates found the determinant of the coefficient matrix in part (a) and solved the resulting quadratic equation with ease. Other approaches generally got nowhere. The work in part (b) was also competently attempted by the majority, apart from silly arithmetical slips which again probably would have been noticed had a very quick check been made.

12 Question : x Any point on the line y = x + 1 has vector position x x The image of this point through TA is x + 1 xx1 x1 = = x+ 4x+ x+ x' = x 1 x= 1 + x' y' = x+ y' =1 x' + = x' + 1 The image of the line y = x + 1 is the line y = x+ 1 b)the area scale factor of the transformation T is det( B) = 6 = 1 1 So the area of P'Q'R'S' is 4. 1= 4.cm 1 1 ct ) C = TA TB = = The transformation is a shear parallel to the x-axis which maps (1,1) into (,1) B Exam report Rather bizarrely, the final bit of part (a) proved to be the most common difficulty on the paper. Having found the image of (x, x + 1) to be (x 1, x), hardly anyone managed to deduce that the equation of the image-line was y = 1 x. Parts (b) and (c) were handled very well indeed, although a few candidates tried BA rather than AB in part (c). The message as to what is an acceptable way to describe a shear has been stated often in recent years reports, and this message has clearly been picked up by nearly all centres: the mapping of a point (not on the line of invariant points) to its image was noted far more regularly than in previous sessions, though there are still some rather spurious references to scale factor spurious in that it is not easy to assign to it an obvious significance or role in the proceedings; indeed, it is not easy even to decide what it is in cases where the shear is not parallel to one of the coordinate axes.

13 Question 6: ai ) )The plane are perpendicular when the normal vectors are orthogonal: nn. '=0 6 4p+ 1. p = 0 4 p+ 6 p+ 6 + = 0 1 1p + 14 = 0 p = ii)the plane are parallel when the normal vectors are linearly dependent: n= kn' Considering the "z" component we need to have k =. and (4p + 1) = 6 and ( p ) = 1 1 p = and p = b) p = 4 x 6 i) y. = 4 6x y+ z = 4 z x 17 y. = 7 17x + y + z = 7 z 1 ii)to find an equation of the line, we need a point and a vector. Let solve these equations simultaneously by choosing x = 0 y+ z = 4 l1 Thisgives : y+ z =7 l l1l gives 7y = 6 or y =8 T he point (0,-8,9) belong to the line. l + l gives 7z = 6 or z = i j k A direction vector to the line is = 6 = 7i+ 8j+ 6k Another direction vector is i4j9k 0 1 An equation of the line of intersection is r = 8 + λ c) A direction vector of the plane is -i+ 4j+ 9k 0 0 Another one is = 0i+ 1j+ 1k An equation of the plane is r = 8 + λ 4 + µ 1 or r= 8 + λ 4 + µ Question 6 and 7 Exam report The structure of these questions proved very helpful to candidates, and those who were reasonably careful could generally score at least 1 of question 6 s 16 marks and 16 of question 7 s 18 marks without any difficulty. The main hurdle arose in question 6, where many candidates failed to realise in part (b) that they had already worked out the eigenvalues of M in part (a), and thus they went ahead and started all over again in an effort to find, and then solve, a cubic characteristic equation. This was all a bit of a waste of time and frequently not as successful as their former effort.

14 Question 7: 16 q 7 l 4 q 4 q 0 l + l a) 1 1q 7 l = 1 1q 7 l = (4 q) 1 1q ql q l q ii) = (4 q) q 1 1 1q 7 = (4 q)( q11)( q10) q bi ) ) = M = = 0 = ii)the other eigenvalues of M are 11 and 10 x x x For λ=11, let solve M y = 11 y or ( M 11 I) y = 0 z z z x+ y+ 7z = 0 1 This gives 1x 1y 7z = 0 and an " obvious" solution is 1 6x+ 6y z = 0 0 x x x For λ=10, let solve M y = 10 y or ( M 10 I) y = 0 z z z 6x+ y+ 7z = 0 x = y from l 7 This gives 1x 11y 7z = 0 7z = y from l1 this gives 7 6x + 6y = 0 Let ' s choose z 1 1 = c) Any line with an eigenvector as direction vector and going through O is invariant. x y z x y for example : = = or ( x = y and z = 0) or = = z Exam report Grade boundaries Grade A B C D E Mark Max