Question

tinh nhanh nang cao

1+1/3+1/6+1/12+1/24+1/48+1/80+1/160

Answer 1

1+1/3+1/6+1/12+1/48+1/80+1/160 = (1+1/3+1/6+1/12+1/24+1/48)+1/80+1/160

Tách bt thành 2 tổng:

Tổng thứ 1: A=1+1/3+1/6+1/12+1/24+1/48

                 2A = 2 + 2/3+1/3+1/6+1/12+1/24

                    A= (2+2/3+1/3+1/6+1/12+1/24)-(1+1/3+1/6+1/12+1/24+1/48)=1+2/3 - 1/48 = 79/48

1/80+1/160= 3/160

Ta có : 79/48 + 3/160 = 799/480