数学简便计算1/1x2x3+1/2x3x4+1/3x4x5……+1/20x21x22=?

数学简便计算1/1x2x3+1/2x3x4+1/3x4x5……+1/20x21x22=?
数学简便计算
1/1x2x3+1/2x3x4+1/3x4x5……+1/20x21x22=?

数学简便计算1/1x2x3+1/2x3x4+1/3x4x5……+1/20x21x22=?
1/1×2×3=1/2×(1/1×2-1/2×3)
其他以此类推
所以原式=1/2×(1/1×2-1/2×3+1/2×3-1/3×4+……+1/20×21-1/21×22)
=1/2×(1/1×2-1/21×22)
=115/462