1*2+2*3+3*4+4*5......+98*99+99*100-1*1-2*2-3*3-4*4-......99*99=1*1+2*2+3*3+---+99*99+1+2+3+-----+99-(1*1+2*2+3*3+----+99*99)=1+2+3+-----+99=100*99/2=4950
式子可以化简成1+2+3+4+。。。+99=4950
49501+2+3...+99=4950
