`12, (3 - 5x)(9 + 15x + 25) = 0`
`=> 3 - 5x = 0 => 5x = 3 => x = 3/5`
`=> 9 + 15x + 25 = 0 `
`=> 15x = -34 => x = -34/15`
Vậy `x = 3/5` và `x = -34/15`
`13, 64 - (2x + 3)^2`
`= 8^2 - (2x + 3)^2`
`= [8 - (2x + 3)] . [8 + (2x + 3)]`
`= (8 - 2x - 3) . (8 + 2x + 3)`
`= (-2x + 5) . (2x + 11)`
Gửi bạn nha