【1】1x2+2x3+3x4+...+10x11=10×11×12/3=440【2】1x2+2x3+3x4+...+nx[n+1]=n(n+1)(n+2)/3【3】请类比以上形式,尝试连续三个字然数的乘积的规律并计算1x2x3+2x3x4+3x4x5+...+7x8x9=7×8×9×10/4=1260