f(x)的导函数为:
f'(x)=lim(x→0)[f(x+Δx)-f(x)]/Δx
=lim(x→0)[C(n,0)x^n+C(n,1)x^(n-1)Δx+•••
+C(n,r)x^(n-r)Δx^r+•••+C(n,n)Δx^n-x^n]/Δx
=lim(x→0)C(n,1)x^(n-1)+C(n,2)x^(n-2)Δx+•••
+C(n,r)x^(n-r)Δx^(r-1)+•••+C(n,n)Δx^(n-1)
=C(n,1)x^(n-1)
=nx^(n-1)
f(x)=x^n,(n∈N+)在x=a处的导数为f'(a)=na^(n-1)