If we have an equation such as (x+y)^n, then the expanded equation would be: (nP0)x^(n)*y^(0)+(nP1)x^(n-1)*y^(1)+(nP0)x^(n-2)*y(2)+(nP3)x^(n-3)*y(3) ... (nPn-1)x^(1)*y^(n-1)+(nPn)x^(0)*y^(n). Note the notation (aPb) here means "a choose b". Or in summation form:
(x+y)^n=Σ((nPk)x^(n-k)*y^k, k, 0, n)