1方+2方+3方+···+n方 从正面推导怎么推
问题描述:
1方+2方+3方+···+n方 从正面推导怎么推
答
n(n+1)(n+2)-(n-1)n(n+1)=3n²+3n,3(1²+2²+3²++++n²)+3(1+2+3++++n)=n(n+1)(n+2)-(n-1)n(n+1)+(n-1)n(n+1)-(n-2)(n-1)n+++++2x3x4-1x2x3,于是3(1²+2...