Question 668505
(x+y)^4 = (4 choose 0)x^4*y^0 + (4 choose 1)x^3*y^1 + (4 choose 2) x^2y^2 + (4 choose 3) x^1*y^3 + (4 choose 4) x^0*y^4 = {{{x^4 + 4x^3y + 6x^2y^2 + 4xy^3 + y^4}}}