a-2a+3a-4a+5a-6a+7a-8a+9a-10a+11a.+99a-100a=

问题描述:

a-2a+3a-4a+5a-6a+7a-8a+9a-10a+11a.+99a-100a=

-a×50=-50a

-50a
原式=(a-2a)+(3a-4a)+……(99a-100a)=-50a