1*2*3+2*3*4+'''+n(n+1)(n+2)=?
问题描述：
1*2*3+2*3*4+'''+n(n+1)(n+2)=?
答
n*(n+1)*(n+2)=n³+3n²+2n1³+……+n³=n²(n+1)²/41²+……+n²=n(n+1)(2n+1)/61+……+n=n(n+1)/2所以原式=n²(n+1)²/4+3n(n+1)(2n+1)/6+2n(n+1)/2=n(n+1)(n+2)(n+3)/4...