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Questions  

The sum of the coefficients of all the integral powers of x in the expansion of (1+2x)80 is

a
12380+1
b
12380−1
c
380+1
d
380-1

detailed solution

Correct option is A

The coefficients of the integral powers of x are 80C0,80C2⋅22,80C4⋅24,…,80C80⋅280Now, (1+2)80=80C0+80C1⋅2+80C2⋅22+…+80C80⋅280           ……. (1)and (1−2)80=80C0−80C12+80C2⋅22−…+80C80⋅280               …….. (2)Adding Eq. (1) and (2), we get380+1=2 80C0+80C2⋅22+80C4⋅24+…+80C80⋅280∴ 80C0+80C2⋅22+80C4⋅24+…+80C80⋅280=12380+1

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