Question 403443
The expansion {{{(a+b)^n}}} is given by


{{{(nC0)a^n + (nC1)a^(n-1)b + (nC2)a^(n-2)b^2}}} + ... + {{{nCn(b^n)}}} where {{{nCk = n!/(n-k)!k!}}}. Here,


{{{(x+y)^4 = (4C0)(x^4) + (4C1)(x^3)y}}} + ... + {{{(4C4)(y^4)}}}


= {{{x^4 + 4x^3y + 6x^2y^2 + 4xy^3 + y^4}}}