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