If the co-efficient of x 7 and x 8 in the expansion of 2 + x 3 n are equal, then the value of n is equal to :

Question

If the co-efficient of x 7 and x 8 in the expansion of 2 + x 3 n are equal, then the value of n is equal to :,

MARKS App · Accepted Answer

We have, the co-efficient of x 7 and x 8 in the expansion of 2 + x 3 n are equal. Therefore, C 7 n 2 n - 7 1 3 7 = C 8 n 2 n - 8 1 3 8 ⇒ n - 7 = 48 ⇒ n = 55 .

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