Question #10746

1 Answer
A. S. Adikesavan
Dec 25, 2016

-1024

Explanation:

(1+2x-x^2)^4

=(2-(1-x)^2)^4

= terms that do not contribute to the coefficient of #x^7

  • the last term ((2-x)^2)^4#, using binomial expansion

So, the coefficient of x^7

= the coefficient in the expansion of ((2-x)^2)^4)=(2-x)^8

=-8C_7 2^7=8 X 128=1024, using binomial expansion

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