Bài `1 :`
`a) 2/9 - 7/8 . x = 1`
`=> 7/8 . x = -7/9`
`=> x = -7/9 : 7/8`
`=> x = -8/9`
`b) 4/5 + 7/6 : x = 1/6`
`=> 7/6 : x = -19/30`
`=> x = 7/6 : -19/30`
`=> x = 35/-19`
`c) 5/9 : x - 3 = -2/7`
`=> 5/9 : x = 19/7`
`=> x = 5/9 : 19/7`
`=> x = 35/171`
`d) 2/5 . x + 1/3 = 1/5`
`=> 2/5 . x = -2/15`
`=> x = -2/15 : 2/5`
`=> x = -1/6`
Bài `2 :`
`a) 3/4 : ( 1/2 : 4/5 )`
`= ( 3/4 : 1/2 ) : 4/5`
`= 3/2 : 4/5`
`= 15/8`
`b) ( 7/12 . 9/14 ) : 1/2`
`= ( 7/12 : 1/2 ) . 9/14`
`= 7/6 . 9/14`
`= 3/4`
`c) ( 7/12 . 9/14 ) : ( 1/2 . 6/5 )`
`= \frac{ 7.9}{12.14} : \frac{1.6}{2.5}`
`= \frac{7.9.2.5}{12.14.1.6}`
`= 5/48`
Bài `3 :`
`\frac{ 3/4 + 3/5 + 3/7 - 3/11}{6/4 + 6/5 + 6/7 - 6/11}`
`= \frac{ 3( 1/4 + 1/5 + 1/7 - 1/11 )}{ 6( 1/4 + 1/5 + 1/6 - 1/11)}`
`= 3/6 = 1/2`