a=-1 求a-2a+3a-4a+5a-6a+...+99a-100a

问题描述:

a=-1 求a-2a+3a-4a+5a-6a+...+99a-100a

a-2a+3a-4a+5a-6a+...+99a-100a
=a﹙1-2+3-4+···+99-100﹚
=-50a
=50