the binomial expansion - solutions
TRANSCRIPT
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AQA Core 2 Sequences and series
1 of 2 15/01/13 MEI
Section 4: The binomial expansion Solutions to Exercise
1. Pascals triangle: 1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
(i) 6 6 5 4 3 2( 1) 6 15 20 15 6 1x x x x x x x
(ii) 5 5 4 1 3 2 2 3 4 5
5 4 3 2
5 4 3 2
( 2) 5 ( 2) 10 ( 2) 10 ( 2) 5 ( 2) ( 2)
5 2 10 4 10 8 5 16 32
10 40 80 80 32
x x x x x x
x x x x x
x x x x x
(iii) 4 4 3 2
4 3 2
4 3 2
(2 1) (2 ) 4(2 ) 6(2 ) 4(2 ) 1
16 4 8 6 4 8 1
16 32 24 8 1
x x x x x
x x x x
x x x x
(iv) 3 3 2 2 3
2 3
2 3
(2 3 ) 2 3(2) ( 3 ) 3(2)( 3 ) ( 3 )
8 3 4 3 3 2 9 27
8 33 54 27
x x x x
x x x
x x x
2. (i) 8 8 7 6
3
1 2 38 7 56
(ii) 9 9 9 8
5 4
27 6
1 2 3 49 2 7 126
(iii) 12 12
4
11 10 59
1 2
3 411 9 5 495
(iv) 20 20 20
18 2
1019
1 2
10 19 190
3. (i) Term in x4
4 4 415 15 14 13 12(2 ) 16 21840
4 1 2 3 4x x x
Coefficient of x4 is 21840
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AQA C2 Series 4 Exercise solutions
2 of 2 15/01/13 MEI
(ii) Term in x23 2 23 25 2 232
23 23
25(3) ( ) (3) ( )
23
25 249 2700
1 2
x C x
x x
Coefficient of x23 is -2700.
(iii) Term in x 4 6
6 2
4
10 10 9 8 71210
4 1 2 3 4
xx xx x
Coefficient of x2 is 210.
4. 4 2(1 ) 1 4 6 ...x x x 7 2(1 ) 1 7 21 ...x x x
4 7 2 2
2 2
2 2 2
2
(1 ) (1 ) 1 4 6 ... 1 7 21 ...
(1 7 21 ) 4 (1 7 ) 6 ...
1 7 21 4 28 6 ...
1 3 ...
x x x x x x
x x x x x
x x x x x
x x
5. (i) 15 2 215 14
(1 ) 1 15 ... 1 15 105 ...1 2
x x x x x
(ii) Putting x = 0.01: 15 2
15
(1 0.01) 1 15 0.01 105 0.01 ...
0.99 1 0.15 0.0105 ... 0.8605
(iii) Percentage error 15
15
0.8605 0.99100 0.051%
0.99
6. (i) 9 2 3
9 2 3212 2
9 8 9 8 71 1 9 ...2 2 1 2 2 1 2 3 2
1 9 ...
x x x x
x x x
(ii) Putting x = 0.1: 9
9 2 3212 2
9
0.11 1 0.1 9 0.1 0.1 ...2
1.05 1 0.45 0.09 0.0105 ... 1.5505
(iii) Percentage error 9
9
1.5505 1.05100 0.053%
1.05