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 DExplanation: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