Bài 1:

`(3x + 1)^2 - 9(x + 2)^2 = -5`

`<=> 9x^2 + 6x + 1 - 9(x^2 + 4x + 4) = -5`

`<=> 9x^2 + 6x + 1 - 9x^2 - 36x - 36 = -5`

`<=> -30x - 35 = -5`

`<=> -30x = 30`

`<=> x = -1`

Vậy `x = -1`

Bài 2:

a) `(3x-5)^2`

`= (3x)^2 - 2 * 3x * 5 + 5^2`

`= 9x^2 - 30x + 25`

b) `(sqrt2 x - 4)^2`

`= (sqrt2 x)^2 - 2 * sqrt2 x * 4 + 4^2`

`= 2x^2 - 8 sqrt2 x + 16`

c) `4x^2 + 4x + 1`

`= (2x)^2 + 2 * 2x * 1 + 1^2`

`= (2x + 1)^2`

d) `x^2 + 2x + 1`

`= x^2 + 2 * x * 1 + 1^2`

`= (x+1)^2`

`\ttcolor{cyan}{#PUyen}`