100²-99²+98²-97²+96²-95²+...+2²-1²
=(100+99)(100-99)+(98+97)(98-97)+……(2+1)(2-1)
=100+99+98+……+2+1
=(100+1)×100÷2
=101×50
=5050
100²-99²+98²-97²+96²-95²+...+2²-1²
=(100+99)(100-99)+(98+97)(98-97)+……(2+1)(2-1)
=100+99+98+……+2+1
=(100+1)×100÷2
=101×50
=5050