Engineering
Mathematics
Introduction to Binomial Theorem
Question

The smallest natural number n, such that the coefficient of x in the expansion of (x2+1x3)n is nC23, is

58

35

23

38

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Solution

Tr+1=∑r=0nnCrx2n−2r.x−3r

2n – 5r = 1 ⇒ 2n = 5r + 1 for r = 15, n = 38 smallest value of n is 38.