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C1 Binomial Expansion

I am stuck on this question in my textbook.

Find the coefficient of x^5 in the expansion of (2+x)^7

I got the answer as 21 using 7C5, but the answer at the back of the book says its 84

EDIT: C2 not C1
Original post by danbomb123
I am stuck on this question in my textbook.

Find the coefficient of x^5 in the expansion of (2+x)^7

I got the answer as 21 using 7C5, but the answer at the back of the book says its 84

EDIT: C2 not C1


You missed the power of 2.


7C5x527−5^7C_5x^52^{7-5}
(edited 9 years ago)
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Avatar for Nels98
Nels98
2
7C5 x 2^2

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