Question

1/1×2×3+1/2×3×4+、、、+1/20×21×22=?

Answer 1

1/1*2*3+1/2*3*4+1/3*4*5+1/4*5*6+……+1/20*21*22=0.5(1/1*2-1/2*3+1/2*3-1/3*4....)=0.5*(0.5-1/21*22)