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If (1 + ax)^n= 1 +8x+ 24x^2 +..... then...

If `(1 + ax)^n= 1 +8x+ 24x^2 +.....` then the value of `a+n` is

A

4

B

6

C

8

D

10

Text Solution

Verified by Experts

The correct Answer is:
6
Given,
`(1+ax)^(n)=1+8x+24x^(2) +. . . .`
`implies1+anx+(n(n-1))/(2!)a^(2)x^(2)+ . . .=1+8x+24x^(2)+ . . .`
`thereforean=8 and a^(2)(n(n-1))/(2)=24`
`implies8(8-a)=48`
`implies8-a=6implies a=2`
Hence, `a=2` and `n=4`
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