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What is the coeffiicient of x^2 y^2 in the expansion of (x + y)^4 + (x + 8y)^4?

 Nov 18, 2020
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The answer is \(390 \), I can't think of a good way to do this than just expanding all of it. 

 

Expanding all of these two expressions gives \(2x^4+4097y^4+36x^3y+390x^2y^2 + 2052xy^3\). From this you can clearly see that the coefficient of \(x^2y^2 = 390\).

 Nov 18, 2020

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