计算:-1/2-1/6-1/12-1/20……-1/72-1/90
问题描述：
计算:-1/2-1/6-1/12-1/20……-1/72-1/90
答
-0.9
答
=(-1/1×2)-(1/2×3)+...+(-1/9×10)
=-(1-1/2)-(1/2-1/3)-(1/3-1/4)...-(1/9-1/10)
=-1+1/2-1/2+1/3-1/3+...+1/9-1/9+1/10
=-1+1/10
=-9/10