1、計算:1/1×2+1/2×3+1/3×4+…+1/99×100
1/1×2+1/2×3+1/3×4+…+1/99×100
=1-1/2+1/2-1/3+1/3-1/4+…+1/99-1/100
=1-1/100
=99/100
2、計算:1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+1/(4×5×6)+…+1/(21×22×23)
1/(1×2×3)+1/(2×3×4)+1/(3×4×5)+1/(4×5×6)+…+1/(21×22×23)
=(1/2)【1/(1×2)-1/(2×3)+1/(2×3)-1/(3×4)+1/(3×4)-1/(4×5)+1/(4×5)-1/(5×6)+…+1/(21×22)-1/(22×23)】
=(1/2)【1(1×2)-1/(22×23)】
=(1/2)(126/253)
=63/253