Question

The 5th term of the expansion (2a - 3b)²⁰¹ is

Answer 1

The r

th

term in expansion of (a+x)

n

is given by

n

C

r−1

a

n+1−r

x

r−1

∴ the 5

th

term in the expansion of (2a−

3

b

)

8

is

8

C

4

(2a)

4

3

4

(−b)

4

which equals

81

1120

a

4

b

4