求50²-49²+48²-…-1²的值
问题描述:
求50²-49²+48²-…-1²的值
答
50²-49²+48²-…-1
=(50+49)×(50-49)+(48+47)×(48-47)+……+(2+1)×(2-1)
=50+49+48+47+……+2+1
=(50+1)+(49+2)+……+(25+26)
=51x25
=1275