# The coefficients of three consecutive terms in the expansion of(1+x)n are in the ratio 1:7:42. find  n.

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• -3

Let 1st,2nd and 3rd terms be in the ratio 1:7:42

Therefore,

nC1 x = 7

or, nx = 7  ---------------------- I

nC2 x = 42

or, n(n-1) x2 = 42

or, nx(n-1)x = 42

or, 7(n-1)x = 42

or, 7nx - 7x = 42

or, 49 - 7x = 42

or, x = 1

putting value of x in 1st equation , n = 7

Hence n = 7

• -13

forgot to make it in powers pls understand that way. the second equation is nC2 x2

• -6
the  coeffivicent of three consecutive terms in the expansion of (1+n) nare in the ratio 1:7:42. find n
• -5
all are wrong..
• -11
the answer to this question is very simple all u have to do is just solve
• -1
• -1
This is the correct answer after you find the coefficients using the general formula. to find coefficients use general formula in Tr+1, T(r+1)+1 and T (r+2)+1. • 48

## 1 Answer     • -1
• -1
• 2 • 0
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• 1
Ccccc
• 0
This is the correct answer after you find the coefficients using the general formula. to find coefficients use general formula in Tr+1, T(r+1)+1 and T (r+2)+1. • 1
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