>>54
(fg)^n
= Σ[k=0,n]nCk (f)^(k) (g)^(n-k)
;f= x^2, g=e^x; (f)^k=0, k≧3; (g)^(n-k)=e^x
= fg^(n) + n/1! f'g^(n-1) + n(n-1)/2! f''g^(n-2)
+ n(n-1)(n-2)/3! f''' g^(n-3) + ・・・・n/1!f^(n-1)g' + f^(n)g
= x^2e^x + n(2x)e^x + n(n-1)/2! (2!)e^x + 0 + ・・・+ 0
= (x^2 + 2nx + n(n-1))e^x