Let (1+x)^n=1+a_1x+a_2x^2+ +a_nx^n. If a_1,a_2 and a_3 are in AP, then the value of n is

JEE Main Mathematics question

Let . If and are in AP, then the value of is

Answer: (D)

, , , and gives . Dividing by and simplifying,

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Question ID VK-021023