~ Bạn tham khảo ~
Ta có :
`A = 4/[7.31] + 6/[7.41] + 9/[10.41] + 7/[10.57]`
`=> A = 20/31.35+30/35.41+45/41.50+35/50.57`
`=> A = 5(4/31.35+6/35.41+9/41.50+7/50.57)`
`=> A = 5(1/31-1/35+1/35-1/41+1/41-1/50+1/50-1/57)`
`=> A = 5(1/31-1/57)` `(1)`
Lại có :
`B = 7/19.31 + 5/19.43 + 3/23.43 + 11/23.57`
`=> B=14/38.31+10/38.43+6/46.43+22/46.57`
`=> B = 2(7/31.38+5/38.43+3/43.46+11/46.57)`
`=> B = 2(1/31-1/38+1/38-1/43+1/43-1/46+1/46-1/57)`
`=> B = 2(1/31-1/57)` `(2)`
Từ `(1),(2) => A/B` $= \dfrac{5\bigg(\dfrac1{31}-\dfrac1{57}\bigg)}{5\bigg(\dfrac1{31}-\dfrac1{57}\bigg)}=\dfrac52$
Vậy `A/B = 5/2`
