tìm x: a. (5x+1)^2-(5x+3)(5x-3)=30 b. ( 6x-2)^2+(5x-2)^2-4(3x-1)(5x-2)=0 tlhn, cn, 5vt

`a)`

`(5x+1)^2 – (5x+3)(5x-3) = 30`

`=> [ (5x)^2 + 2 . 5x . 1 + 1^2] – [ (5x)^2 – 3^2] = 30`

`=> (25x^2 + 10x + 1) – (25x^2 – 9) = 30`

`=> 25x^2 + 10x + 1 – 25x^2 + 9  =30`

`=> 10x +10 = 30`

`=> 10x = 20`

`=> x = 2`

Vậy `x=2`

`b)`

`(6x-2)^2 + (5x-2)^2 – 4 . (3x-1)(5x-2) = 0`

`=> [ (6x)^2 – 2 . 6x .2 + 2^2] + [ (5x)^2 – 2  .5x . 2 + 2^2] – (12x -4)(5x-2)=0`

`=> (36x^2 – 24x + 4) + (25x^2 – 20x + 4) – (60x^2 – 24x – 20x + 8) = 0`

`=> 36x^2 – 24x + 4 + 25x^2 – 20x + 4 – 60x^2 + 24x + 20x – 8  =0`

`=> x^2 =0`

`=> x=0`

Vậy `x=0`