1×(-2分之1)＋2分之1×(-3分之1)＋3分之1×(-4分之1)＋…＋99分之1×(-100分之1)
=-(1/1×2+1/2×3+1/3×4+……+1/99×100)
=-(1/1-1/2+1/2-1/3+1/3+1/4-1/4+……-1/99+1/99-1/100)
=-(1-1/100)
=-99/100