50*2-49*2+48*2-47*2+.2*2-1*2怎么计算?
问题描述:
50*2-49*2+48*2-47*2+.2*2-1*2怎么计算?
答
50*50-49*49+48*48.+2*2-1*1
=(50+49)(50-49)+(48+47)(48-47)+-----+(2+1)(2-1)
=99+95+91+.+7+3
=(99+3)×25/2
=51×25
=1275