`e)`
`25x^2- 9 =0`
`=> (5x)^2- 3^2= 0`
`=> (5x-3)(5x+3)=0`
`=>5x-3=0` hoặc `5x+3=0`
`+) 5x - 3 =0 <=> 5x = 3 <=> x= 3/5`
`+) 5x + 3 = 0 <=> 5x = -3 <=> x= -3/5`
Vậy `x \in {3/5 ; -3/5}`
`f)`
`(x+5)^2 - (x+1)(x-1) = 16`
`=> (x^2 + 2 . x . 5 + 5^2) - (x^2 - 1^2) = 16`
`=> (x^2 + 10x + 25) - (x^2 - 1) = 16`
`=> x^2 + 10x + 25 - x^2 + 1 =16`
`=> 10x + 26 = 16`
`=> 10x = -10`
`=> x = -1`
Vậy `x=-1`
`g)`
`(2x+1)^2 - 4(x+2)^2= 9`
`=> [ (2x)^2 + 2 . 2x . 1 + 1^2] - 4 (x^2 + 2 . x . 2 + 2^2) = 9`
`=> (4x^2 + 4x + 1) - 4(x^2 + 4x + 4) = 9`
`=> 4x^2 + 4x + 1 - 4x^2 -16x - 16 = 9`
`=> -12x - 15 = 9`
`=> -12x = 24`
`=> x= -2`
Vậy `x=-2`
`h)`
`(3x-1)^2 + 2(x+3)^2 + 11(x+1)(1-x) = 6`
`=> [ (3x)^2 - 2 . 3x . 1 + 1^2] + 2 (x^2 + 2 . x . 3 + 3^2) + 11 (1^2 - x^2) = 6`
`=> (9x^2 - 6x + 1) + 2 (x^2 + 6x + 9) + 11 (1-x^2)=6`
`=> 9x^2 - 6x + 1 + 2x^2 + 12x + 18 + 11 - 11x^2 = 6`
`=> 6x + 30 =6`
`=> 6x = -24`
`=> x = -4`
Vậy `x=-4`
