cho A = 4/7x31 + 6/7x41 + 9/10x41 + 7/10x57 B= 7/19x31 + 5/19x43 + 3/23x43 + 11/23x57 Tìm tỉ số của A/B

Đáp án:

`A = 4/(7.31) + 6/(7.41) + 9/(10.41) + 7/(10.57 )`

`-> A =  20/(35.31) + 30/(35.41) + 45/(50.41 )+ 35/(50.57 )`

`-> A = 5 . (4/(35.31) + 6/(35.41) + 9/(50.41) + 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)`

`B=7/(19.31)+5/(19.43)+3/(23.43)+11/(23.57)`

`-> B = 14/(38.31) + 10/(38.43 )+ 6/(43.46) + 22/(46.57)`

`-> B = 2 . (7/(38.31) + 5/(38.43 )+ 3/(43.46) + 11/(46.57))`

`->B = 2 . (1/31 - 1/35 + 1/35 - 1/41 + 1/41 - 1/50 + 1/50 - 1/57  )`

`-> B = 2 . (1/31 - 1/57)`       `(2)`

`(1)(2) -> A/B = ` $\dfrac{5.(\dfrac{1}{31} - \dfrac{1}{57})}{2.(\dfrac{1}{31} - \dfrac{1}{57})} = \dfrac{5}{2}$

`#dariana`