What is the coeffiicient of x^2 y^2 in the expansion of (x + y)^4 + (x + 8y)^4?
+179 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 \(x^2y^2 = 390\).
