tính hộ em với : 1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90

Giải thích các bước giải:

`1−5/6+7/12−9/20+11/30−13/42+15/56−17/72+19/90`

`=1−5/(2×3)+7/(3×4)−9/(4×5)+11/(5×6)−13/(6×7)+15/(7×8)−17/(8×9)+10/(9×10)`

`=1−1/2−1/3+1/3+1/4−1/4−1/5+1/5+1/6−1/6−1/7+1/7+1/8−1/8−1/9+1/9+1/10`

`=1−1/2+1/10=1/2+1/10=6/10=3/5`