Giúp mình bài này nhé

`a) 2/5x + 3/7 = -4/5`

`=> 2/5x = -4/5 - 3/7`

`=> 2/5x = -43/35`

`=> x = -43/35 : 2/5`

`=> x = -43/14`

Vậy `x = -43/14`

`b) |x + 1/2| - 3/7 = 2 4/7`

`=> |x + 1/2| = 18/7 + 3/7`

`=> |x + 1/2| = 3`

`=> x + 1/2 = 3` hoặc `x + 1/2 = -3`

`=> x = 5/2` hoặc `x = -7/2`

Vậy `x = 5/2; x = -7/2`

`c) 3^x + \sqrt{4} . 3^(x - 1) = 3^2 . \sqrt{49}`

`=> 3^x + 2 . 3^(x + 1) = 9 . 7`

`=> 3^x + 2 . 3^(x + 1) = 63`

`=> 3^x + 2 . 3^x. 3 = 63`

`=> 3^x + 6 . 3^x = 63`

`=> 3^x . (6 + 1) = 63`

`=> 3^x . 7 = 63`

`=> 3^x = 9`

`=> x = 2`

Vậy `x = 2`