`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`
