Study Materials

NCERT Solutions for Class 11th Mathematics

 

Page 2 of 3

Chapter 8. Binomial Theorem

Exercise 8.2

 

 

 

Exercise 8.2 

Find the coefficient of  

Q1.  x5 in (x + 3)8

Solution:

(x + 3)8

General term nCr an-r br

 n = 8, then

8Cr x8-r 3r x5 = x8-r

5 = 8-r

∴ r = 8-5 = 3

8C3 x8-3 33 = 8C3 x5 33

Coefficient in x5 = 8C3 33

= 1512 

Q2.  a5b7 in (a-2b)12

Solution:

 (a-2b)12

General Term Tr+1 = nCr an-r br

12Cr a12-r br

12 – r = 5  r = 12 – 5 = 7

 a5b7 is 8 term

T8 = 12C7 a5 b7

     = 12C7 a5 (-2b)7

    = - 72 × 11 × 27

    = - 72 × 11 × 128 = - 101376 

Write the general term in the expansion of

Q3. (x2 - y)6

Solution:

General term of (x2 - y)6

n = 6, a = x2, b = (-y) 

General Term Tr +1nCan-r br

=  6Cr (x2)6-r (-y)r

 

Page 2 of 3

 

Chapter Contents: