1-2²+3²-4²+5²-6²+.+99²-100²

1-2²+3²-4²+5²-6²+.+99²-100²

원식
=(1+2)(1-2)+(3+4)(3-4)+.+(99+100)(99-100)
=- (1+2)-(3+4)-(5+6)-.-(99+100)
=- (1+2+3+.+99+100)
=-5050