计算:12-22+32-42+52-62+72-82+92-102=_.
问题描述:
计算:12-22+32-42+52-62+72-82+92-102=______.
答
12-22+32-42+52-62+72-82+92-102=-[(22-12)+(42-32)+(62-52)+(82-72)+(102-92)]=-[(2+1)(2-1)+(4+3)+(4-3)(6+5)(6-5)+(8+7)(8-7)+(10+9)(10-9)]=-[(2+1)×1+(4+3)×1+(6+5)×1+...