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A-level基础数学2009年1月C2试题答案


Mark Scheme (Results) January 2009

GCE

GCE Mathematics (6664/01)

Edexcel Limited. Registered in England and Wales No. 4496750 Registered Office: One90 High Holborn, London WC1V 7BH

January 2009 6664 Core Mathematics C2 Mark Scheme
Question Number 1 Scheme Marks B1, B1 M1 A1 (4) [4]

(3 ? 2 x) 5 = 243 ,

…… + 5 × (3) (?2 x) = ?810 x ……
4

+
Notes

5× 4 3 (3) (?2 x) 2 = 2

+ 1080 x 2

Special cases

First term must be 243 for B1, writing just 35 is B0 (Mark their final answers except in second line of special cases below). Term must be simplified to –810x for B1 The x is required for this mark. The method mark (M1) is generous and is awarded for an attempt at Binomial to get the third term. There must be an x 2 (or no x- i.e. not wrong power) and attempt at Binomial Coefficient and at dealing with powers of 3 and 2. The power of 3 should not be one, but the power of 2 may be one (regarded as bracketing slip). ?5? ? 5? ?5? ?5? So allow ? ? or ? ? or 5C2 or 5C3 or even ? ? or ? ? or use of ‘10’ (maybe from ? 2? ? 3? ? 2? ? 3? Pascal’s triangle) May see 5C2 (3)3 (?2 x) 2 or 5C2 (3)3 (?2 x 2 ) or 5C2 (3)5 (? 2 x 2 ) or 10(3)3 (2 x) 2 which would 3 each score the M1 A1is c.a.o and needs 1080x 2 (if 1080x 2 is written with no working this is awarded both marks i.e. M1 A1.) 243 + 810 x + 1080 x 2 is B1B0M1A1 (condone no negative signs) Follows correct answer with 27 ? 90 x + 120 x 2 can isw here (sp case)– full marks for correct answer Misreads ascending and gives ?32 x 5 + 240 x 4 ? 720 x 3 is marked as B1B0M1A0 special case and must be completely correct. (If any slips could get B0B0M1A0) Ignores 3 and expands (1 ± 2 x)5 is 0/4 243, -810x, 1080x 2 is full marks but 243, -810, 1080 is B1,B0,M1,A0 ? 5? 2 NB Alternative method 35 (1 ? 2 x)5 = 35 ? 5 × 35 × ( 2 x ) + ? ? 35 ( ? 2 x ) + .. is B0B0M1A0 3 3 3 ? 3?
– answers must be simplified to 243 –810x +1080 x 2 for full marks (awarded as before) ? 5? 2 Special case 3(1 ? 2 x)5 = 3 ? 5 × 3 × ( 2 x ) + ? ? 3 ( ? 2 x ) + .. is B0, B0, M1, A0 3 3 3 ? 3? Or 3(1 ? 2 x)5 is B0B0M0A0

6664/01 GCE Mathematics January 2009

2

Question Number 2

Scheme

Marks M1

y = (1 + x)(4 ? x) = 4 + 3x ? x 2

M: Expand, giving 3 (or 4) terms
x3 3

3x ∫ (4 + 3x ? x )dx = 4 x + 2
2

2

?

M: Attempt to integrate
5? ? ? = 20 ? 6? ?

M1 A1

64 ? ? 3 1 ? 125 ? 4 = [...............]?1 = ?16 + 24 ? ? ? ? ? 4 + + ? = 3? ? 2 3? 6 ?

M1 A1

(5) [5]

Notes

M1 needs expansion, there may be a slip involving a sign or simple arithmetical error e.g. 1× 4 = 5 , but there needs to be a ‘constant’ an ‘x term’ and an ‘ x 2 term’. The x terms do not need to be collected. (Need not be seen if next line correct)

Attempt to integrate means that x n → x n +1 for at least one of the terms, then M1 is awarded ( even 4 becoming 4x is sufficient) – one correct power sufficient.
A1 is for correct answer only, not follow through. But allow 2x 2 ? 1 x 2 or any correct 2 equivalent. Allow + c, and even allow an evaluated extra constant term. M1: Substitute limit 4 and limit –1 into a changed function (must be –1) and indicate subtraction (either way round). A1 must be exact, not 20.83 or similar. If recurring indicated can have the mark. Negative area, even if subsequently positive loses the A mark.
Special cases

(i) Uses calculator method: M1 for expansion (if seen) M1 for limits if answer correct, so 0 , 1 or 2 marks out of 5 is possible (Most likely M0 M0 A0 M1 A0 ) (ii) Uses trapezium rule : not exact, no calculus – 0/5 unless expansion mark M1 gained. (iii) Using original method, but then change all signs after expansion is likely to lead to: M1 M1 A0, M1 A0 i.e. 3/5

6664/01 GCE Mathematics January 2009

3

Question Number 3 (a) 3.84, 4.14, 4.58 (b)

Scheme

Marks

(Any one correct B1 B0. All correct B1 B1)

B1 B1

(2)

1 × 0.4, 2 = 7.852

{(3 + 4.58) + 2 ( 3.47 + 3.84 + 4.14 + 4.39 )}
(awrt 7.9)

B1, M1 A1ft A1 (4) [6]

Notes (a)

B1 for one answer correct

Second B1 for all three correct
21 ,

Accept awrt ones given or exact answers so 429 , score the marks. 5 (b) B1 is for using 0.2 or 0.4 as 1 h. 2 2

3 41 ? 369 ? , and ? ? or 5 ? 25 ?

? 429 ? ? ? or ? 25 ?

M1 requires first bracket to contain first plus last values and second bracket to include no additional values from those in the table. If the only mistake is to omit one value from 2nd bracket this may be regarded as a slip an can be allowed ( An extra repeated term forfeits the M mark however) x values: M0 if values used in brackets are x values instead of y values. Separate trapezia may be used : B1 for 0.2, M1 for 1 h(a + b) used 4 or 5 times ( and A1ft all 2 e.g.. 0.2(3 + 3.47) + 0.2(3.47 + 3.84) + 0.2(3.84 + 4.14) + 0.2(4.14 + 4.58) is M1 A0 equivalent to missing one term in { } in main scheme A1ft follows their answers to part (a) and is for {correct expression}

Final A1 must be correct. (No follow through)
Special cases

1 × 0.4(3 + 4.58) + 2(3.47 + 3.84 + 4.14 + 4.39) 2 scores B1 M1 A0 A0 unless the final answer implies that the calculation has been done correctly (then full marks can be given).
Bracketing mistake: i.e.
Need to see trapezium rule – answer only (with no working) is 0/4.

6664/01 GCE Mathematics January 2009

4

Question Number 4

Scheme

Marks

2 log 5 x = log 5 x 2 , ? 4? x ? log ? 2 ? = log 5 ? x ? (5 x ? 4)( x + 1) = 0
x=

( )

log 5 (4 ? x) ? log 5 ( x 2 ) = log 5

4? x x2

B1, M1 M1 A1 dM1 A1 (6) [6]

5 x 2 + x ? 4 = 0 or 5 x 2 + x = 4 o.e. 4 5 (x = ?1)

Notes

B1 is awarded for 2 log x = log x 2 anywhere. A M1 for correct use of log A – log B = log B M1 for replacing 1 by log k k . A1 for correct quadratic

( log(4 ? x) ? log x 2 = log 5 ? 4 ? x ? x 2 = 5 is B1M0M1A0 M0A0)
dM1 for attempt to solve quadratic with usual conventions. (Only award if previous two M marks have been awarded) A1 for 4/5 or 0.8 or equivalent (Ignore extra answer).
Alternative 1

log 5 (4 ? x) ? 1 = 2 log 5 x so log 5 (4 ? x) ? log 5 5 = 2 log 5 x 4? x log 5 = 2 log 5 x 5 then could complete solution with 2 log 5 x = log 5 x 2

M1 M1 B1 A1

( )
4 5

? 4? x? 2 ? ? =x ? 5 ?

5x2 + x ? 4 = 0
x=

Then as in first method (5 x ? 4)( x + 1) = 0
Special cases

(x = ?1)

dM1 A1 (6) [6]

Complete trial and error yielding 0.8 is M3 and B1 for 0.8 A1, A1 awarded for each of two tries evaluated. i.e. 6/6 Incomplete trial and error with wrong or no solution is 0/6 Just answer 0.8 with no working is B1 If log base 10 or base e used throughout - can score B1M1M1A0M1A0

6664/01 GCE Mathematics January 2009

5

Question Number 5 (a)

Scheme

Marks

PQ: m1 =

10 ? 2 (= 2 ) 3 9 ? (?3)

and

QR: m2 =

10 ? 4 9?a

M1 M1 A1 (3)

(b) Alt for (a)

8 6 (*) × = ?1 a = 13 12 9 ? a (a) Alternative method (Pythagoras) Finds all three of the following
m1m2 = ?1 :
2

( 9 ? ( ?3) )

+ (10 ? 2) 2 , (i.e.208) ,

(9 ? a )

2

+ (10 ? 4) 2 ,

( a ? ( ?3 ) )

2

+ (4 ? 2) 2

M1 M1 A1 (3) B1 M1 A1 M1 A1 (5) M1 M1 A1, A1, B1cao (5) [8]

Using Pythagoras (correct way around) e.g. a 2 + 6a + 9 = 240 + a 2 ? 18a + 81 to form equation Solve (or verify) for a, a = 13 (*) (b) Centre is at (5, 3)

(r =) (10 ? 3)
2

2

+ (9 ? 5) 2 or equiv., or d 2 =

(

) (13 ? (? 3))

2

+ ( 4 ? 2) 2

( x ? 5) 2 + ( y ? 3) 2 = 65
Alt for (b)

or x 2 + y 2 ? 10 x ? 6 y ? 31 = 0

Uses ( x ? a) 2 + ( y ? b) 2 = r 2 or x 2 + y 2 + 2 gx + 2 fy + c = 0 and substitutes (-3, 2), (9, 10) and (13, 4) then eliminates one unknown Eliminates second unknown Obtains g = ?5, f = ?3, c = ?31 or
a = 5, b = 3, r 2 = 65

Notes (a) M1-considers gradients of PQ and QR -must be y difference / x difference

(or considers three lengths as in alternative method) M1 Substitutes gradients into product = -1 (or lengths into Pythagoras’ Theorem the correct way round ) A1 Obtains a = 13 with no errors by solution or verification. Verification can score 3/3.
(b) Geometrical method: B1 for coordinates of centre – can be implied by use in part (b)

M1 for attempt to find r 2 , d 2 , r or d ( allow one slip in a bracket). A1 cao. These two marks may be gained implicitly from circle equation M1 for ( x ± 5) 2 + ( y ± 3) 2 = k 2 or ( x ± 3) 2 + ( y ± 5) 2 = k 2 ft their (5,3) Allow k 2 non numerical. A1 cao for whole equation and rhs must be 65 or

(

65 , (similarly B1 must be 65 or

)

2

(

65 , in alternative method for (b))

)

2

6664/01 GCE Mathematics January 2009

6

Question Number Further alternatives

Scheme

Marks M1 M1

(i) A number of methods find gradient of PQ = 2/3 then give perpendicular gradient is –3/2 This is M1 They then proceed using equations of lines through point Q or by using 4 ? 10 3 gradient QR to obtain equation such as = ? M1 (may still have a ?9 2 x in this equation rather than a and there may be a small slip) They then complete to give (a )= 13 A1 (ii) A long involved method has been seen finding the coordinates of the centre of the circle first. This can be done by a variety of methods Giving centre as (c, 3) and using an equation such as (c ? 9) 2 + 7 2 = (c + 3) 2 + 12 (equal radii) 3?6 3 or = ? M1 (perpendicular from centre to chord bisects chord) 2 c ?3 Then using c ( = 5) to find a is M1 Finally a = 13 A1 (iii) Vector Method: States PQ. QR = 0, with vectors stated 12i +8j and (9 – a)i + 6j is M1 Evaluates scalar product so 108 – 12 a + 48 = 0 (M1) solves to give a = 13 (A1)

A1 M1

M1 A1 M1 M1 A1

6664/01 GCE Mathematics January 2009

7

Question Number 6 (a)

Scheme

Marks M1 A1 M1 A1 A1cso (5) M1 A1ft A1 cso M1 A1 M1 A1 A1cso M1 A1ft A1 cso (3) [8] (5) (3) [8]

f (2) = 16 + 40 + 2a + b or f (?1) = 1 ? 5 ? a + b

Finds 2nd remainder and equates to 1st ? 16 + 40 + 2a + b = 1 ? 5 ? a + b
(b)

a = ?20 f (?3) = (?3) 4 + 5(?3) 3 ? 3a + b = 0

81 – 135 + 60 + b = 0 gives b = -6
Alternative for (a)

(a) Uses long division, to get remainders as b + 2a + 56 or b – a - 4 or correct equivalent Uses second long division as far as remainder term, to get b + 2a + 56 = b – a - 4 or correct equivalent a = ?20

Alternative for (b)

(b) Uses long division of x 4 + 5 x3 ? 20 x + b by (x + 3) to obtain x3 + 2 x 2 ? 6 x + a + 18 ( with their value for a ) Giving remainder b + 6 = 0 and so b = -6

M1 : Attempts f( ±2 ) or f( ±1 ) A1 is for the answer shown (or simplified with terms collected ) for one remainder M1: Attempts other remainder and puts one equal to the other A1: for correct equation in a (and b) then A1 for a = ?20 cso (b) M1 : Puts f (±3) = 0 A1 is for f( -3) = 0, (where f is original function), with no sign or substitution errors (follow through on ‘a’ and could still be in terms of a ) A1: b = -6 is cso. Alternatives (a) M1: Uses long division of x 4 + 5 x 3 + ax + b by (x ±2 ) or by (x ±1 ) as far as three term quotient A1: Obtains at least one correct remainder M1: Obtains second remainder and puts two remainders (no x terms) equal A1: correct equation A1: correct answer a = -20 following correct work. (b) M1: complete long division as far as constant (ignore remainder)
Notes (a)

A1ft: needs correct answer for their a A1: correct answer Beware: It is possible to get correct answers with wrong working. If remainders are equated to 0 in part (a) both correct answers are obtained fortuitously. This could score M1A1M0A0A0M1A1A0

6664/01 GCE Mathematics January 2009

8

Question Number 7 (a) (b)

Scheme

Marks M1 A1 M1 A1 M1 A1ft (2) (2)

1 2 1 r θ = × 6 2 × 2.2 = 39.6 cm 2 2 2 ? 2π ? 2.2 ? = ? π ? 1.1 = 2.04 (rad) ? 2 ? ? (c) ?DAC =

( )

1 × 6 × 4 sin 2.04 (≈ 10.7) 2 Total area = sector + 2 triangles = 61
(a)

(cm )
2

M1 A1

(4) [8]

M1: Needs θ in radians for this formula. Could convert to degrees and use degrees formula. A1: Does not need units. Answer should be 39.6 exactly. Answer with no working is M1 A1. This M1A1 can only be awarded in part (a). M1: Needs full method to give angle in radians A1: Allow answers which round to 2.04 (Just writes 2.04 – no working is 2/2)

(b) (c)

1 × 6 × 4sin A (if any other triangle formula e.g. 1 b × h is used the method 2 2 must be complete for this mark) (No value needed for A, but should not be using 2.2) A1: ft the value obtained in part (b) – need not be evaluated- could be in degrees M1: Uses Total area = sector + 2 triangles or other complete method A1: Allow answers which round to 61. (Do not need units)
M1: Use

Special case degrees: Could get M0A0, M0A0, M1A1M1A0 Special case: Use ? BDC – ? BAC Both areas needed for first M1 Total area = sector + area found is second M1 NB Just finding lengths BD, DC, and angle BDC then assuming area BDC is a sector to find area BDC is 0/4

6664/01 GCE Mathematics January 2009

9

Question Number 8 (a) (b)

Scheme

Marks

4(1 ? cos 2 x) + 9 cos x ? 6 = 0 (4 cos x ? 1)(cos x ? 2) = 0
x = 75.5

4 cos 2 x ? 9 cos x + 2 = 0 (*) cos x = ..., 1 4

M1 A1 M1 A1 B1

(2)

(α ) or 720 - α

360 ? α , 360 + α 284.5, 435.5, 644.5
(a) (b)

M1, A1

M1 (6) [8]

M1: Uses sin 2 x = 1 ? cos 2 x (may omit bracket) not sin 2 x = cos 2 x ? 1 A1: Obtains the printed answer without error – must have = 0 M1: Solves the quadratic with usual conventions A1: Obtains ? accurately- ignore extra answer 2 but penalise e.g. -2. B1: allow answers which round to 75.5 M1: 360 ? α ft their value, M1: 360 + α ft their value or 720 - α ft A1: Three and only three correct exact answers in the range achieves the mark In part (b) Error in solving quadratic (4cosx-1)(cosx+2) Could yield, M1A0B1M1M1A1 losing one mark for the error

Special cases

Works in radians: Complete work in radians :Obtains 1.3 B0. Then allow M1 M1 for 2π ? α , 2π + α or 4π ? α Then gets 5.0, 7.6, 11.3 A0 so 2/4 Mixed answer 1.3, 360 – 1.3, 360 + 1.3, 720 – 1.3 still gets B0M1M1A0

6664/01 GCE Mathematics January 2009

10

Question Number 9 (a)

Scheme

Marks

Initial step: Two of: a = k + 4, ar = k , ar 2 = 2k ? 15 k 2k ? 15 2k ? 15 Or one of: r = , , r= , r2 = k +4 k k +4 Or k = (k + 4)(2k ? 15) or even k 3 = (k + 4)k (2k ? 15)
k 2 = (k + 4)(2k ? 15) , so k 2 = 2k 2 + 8k ? 15k ? 60

M1

M1, A1

Proceed to k 2 ? 7 k ? 60 = 0
(b)

(*)

A1

(4)

(k ? 12)(k + 5) = 0
(c) (d)

k = 12

(*)

M1 A1

(2)

Common ratio:

k 2k -15 12 ? 3 ? or or 0.75 ? = ?= 16 ? 4 k +4 k ?

M1 A1 M1 A1

(2) (2) [10]

a 16 = = 64 1 1? r 4

( )

(a) M1: The ‘initial step’, scoring the first M mark, may be implied by next line of proof

M1: Eliminates a and r to give valid equation in k only. Can be awarded for equation involving fractions. A1 : need some correct expansion and working and answer equivalent to required quadratic but with uncollected terms. Equations involving fractions do not get this mark. (No fractions, no brackets – could be a cubic equation) A1: as answer is printed this mark is for cso (Needs = 0) All four marks must be scored in part (a) (b) M1: Attempt to solve quadratic A1: This is for correct factorisation or solution and k = 12. Ignore the extra solution (k = ?5 or even k = 5), if seen. Substitute and verify is M1 A0 Marks must be scored in part (b) (c) M1: Complete method to find r Could have answer in terms of k A1: 0.75 or any correct equivalent Both Marks must be scored in (c) (d) a M1: Tries to use , (even with r>1). Could have an answer still in terms of k. 1? r A1: This answer is 64 cao.

6664/01 GCE Mathematics January 2009

11

Question Number 10 (a)

Scheme

Marks B1

2π rh + 2π r 2 = 800
h= 400 ? π r 2 , πr ? 400 ? π r 2 V = π r2? ? πr ? ? ? = 400r ? π r 3 ? ? (*)

M1, M1 A1 (4) M1 A1

(b)

dV = 400 ? 3π r 2 dr
400 ? 3π r 2 = 0 r 2 = ..., r= 400 3π

( = 6.5 (2 s.f.) )

M1 A1 M1 A1 (6) M1 A1

800 400 cm 3 3 3π (accept awrt 1737 or exact answer) (c) d 2V = ?6π r , Negative, ∴maximum dr 2 (Parts (b) and (c) should be considered together when marking)

V = 400r ? π r 3 = 1737 =

( )

(2) [12]

Other methods for part (c):

Either:M: Find value of

dV dr

on each side of “ r =

400 3π

” and consider sign. , and conclude max.

A: Indicate sign change of positive to negative for Or: M: Find value of V on each side of “ r =
400 3π

dV dr

” and compare with “1737”.

A: Indicate that both values are less than 1737 or 1737.25, and conclude max.
Notes

B1: For any correct form of this equation (may be unsimplified, may be implied by 1st (a) M1) M1 : Making h the subject of their three or four term formula M1: Substituting expression for h into π r 2 h (independent mark) Must now be expression in r only. A1: cso (b) M1: At least one power of r decreased by 1 A1: cao dV M1: Setting =0 and finding a value for correct power of r for candidate dr A1 : This mark may be credited if the value of V is correct. Otherwise answers should round to 6.5 (allow ±6.5 )or be exact answer M1: Substitute a positive value of r to give V A1: 1737 or 1737.25….. or exact answer

6664/01 GCE Mathematics January 2009

12

(c)

M1: needs complete method e.g.attempts differentiation (power reduced) of their first derivative and considers its sign A1(first method) should be ?6π r (do not need to substitute r and can condone wrong r if found in (b)) Need to conclude maximum or indicate by a tick that it is maximum. Throughout allow confused notation such as dy/dx for dV/dr

Alternative for (a)

A = 2π r 2 + 2π rh ,

Then V = 400r ? π r is M1 A1

A 2 3

× r = π r 3 + π r 2 h is M1 Equate to 400r

B1

6664/01 GCE Mathematics January 2009

13


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