Find the coefficient of a5b7 in (a – 2b)12

Asked by Abhisek | 1 year ago |  123

#### 1 Answer

##### Solution :-

The general term Tr+1 in the binomial expansion is given by Tr+1 = r an-r br

Here a = a, b = -2b & n =12

Substituting the values, we get

Tr+1 = 12Cr a12-r (-2b)r………. (i)

To find a5

We equate a12-r =a5

r = 7

Putting r = 7 in (i)

T8 = 12C7 a5 (-2b)7

$$T_8=\dfrac{12!}{7!5!}\times a^5\times (-2)^7b^7$$

= -101376 a5 b7

Hence the coefficient of a5b7= -101376

Answered by Pragya Singh | 1 year ago

### Related Questions

#### Find the term independent of x in the expansion of (3/2 x2 – 1/3x)9

Find the term independent of x in the expansion of $$(\dfrac{3}{2x^2} – \dfrac{1}{3x})^9$$

Class 11 Maths Binomial Theorem View Answer

#### Find the middle term in the expansion of (x – 1/x)2n+1

Find the middle term in the expansion of $$(x-\dfrac{ 1}{x})^{2n+1}$$

Class 11 Maths Binomial Theorem View Answer

#### Find the middle term in the expansion of (1 + 3x + 3x2 + x3)2n

Find the middle term in the expansion of (1 + 3x + 3x2 + x3)2n

Class 11 Maths Binomial Theorem View Answer

#### Find the middle term in the expansion of (1 – 2x + x2)n

Find the middle term in the expansion of (1 – 2x + x2)n

Class 11 Maths Binomial Theorem View Answer

#### Find the middle term in the expansion of (x/a – a/x)10

Find the middle term in the expansion of $$(\dfrac{x}{a} – \dfrac{a}{x})^{10}$$

Class 11 Maths Binomial Theorem View Answer