求导得y'=(n+1)x^n
将x=1代入得切线的斜率为n+1
切线的方程为y-1=(n+1)(x-1)
令y=0得x=-1/(n+1) +1=n/(n+1)
所以xn=n/(n+1)
x1x2x3...xn
=(1/2)(2/3)(3/4)……[n/(n+1)]
=1/(n+1)