已知|ab+2|+|a+1|=0,求下式的值:1/(a−1)(b+1)+1/(a−2)(b+2)…+1/(a−2000)(b+2000).

问题描述:

已知|ab+2|+|a+1|=0,求下式的值:

1
(a−1)(b+1)
+
1
(a−2)(b+2)
…+
1
(a−2000)(b+2000)

∵|ab+2|+|a+1|=0,且|ab+2|≥0,|a+1|≥0,∴ab+2=0,且a+1=0,∴a=-1,b=2.∴原式=1−2×3+1−3×4+…+1−2001×2002=-(12×3+13×4+…+12001×2002)=-(12-13+13-14+…+12001-12002)=-12+12002=-5001001....