Question

If in the expansion of (x⁴ - 1/3)¹⁵, x^-17 occurs in r^th term, then 

A. r = 10 

B. r = 11 

C. r = 12 

D. r = 13

Answer 1

Option : (C)

Given :

(x⁴ - 1/x³)¹⁵

⇒ x⁴(15-k)-3k = x -17 

⇒ 60-4k-3k = -17 

⇒ -7k = -77 

⇒ k = 11 

So, the term is 12^th term.