Discussion Forum



1)

 The coefficient of x9   in the expansion of  (1+x)(1+x2)+(1+x3).......(1+x100)  is


A) 5

B) 6

C) 9

D) 8

Answer:

Option D

Explanation:

The coefficient of x9   in the expansion of 

      (1+x)(1+x2)+(1+x3).......(1+x100)  = Terms having x9

 

 =  [I99.x9,I98.x.x8,I98.x2.x7,I98.x3.x6I98.x4.x5

          I97.x.x2.x6I97.x.x3.x5I97.x2.x3.x4]

  ∴ coefficient of x9=8