1) x² + 2x - 3x - 6 = 0 => x² - x - 6 = 0 => (x - 3)(x + 2) = 0 => x = 3 hoặc x = -2 2) x + 2(0x - x) - 20 = 0 => x - 3x - 20 = 0 => -2x - 20 = 0 => -2x = 20 => x = -10 3) x² - 4x² - x + 4 = 0 => -3x² - x + 4 = 0 => (3x - 4)(x + 1) = 0 => x = 4/3 hoặc x = -1 4) 2x² - 2x = (x - 1)² => 2x² - 2x = x² - 2x + 1 => x² = 1 => x = 1 hoặc x = -1 5) 3(x - 6)² = 60 - 10x => 3(x² - 12x + 36) = 60 - 10x => 3x² - 36x + 108 = 60 - 10x => 3x² - 26x + 48 = 0 => (3x - 4)(x - 12) = 0 => x = 4/3 hoặc x = 12 6) 2(x - 5) - x² + 25 = 0 => 2x - 10 - x² + 25 = 0 => -x² + 2x + 15 = 0 => (x - 5)(x + 3) = 0 => x = 5 hoặc x = -3 7) x² - 8x + 3x - 24 = 0 => x² - 5x - 24 = 0 => (x - 8)(x + 3) = 0 => x = 8 hoặc x = -3 8) x² + 10x - 2x - 20 = 0 => x² + 8x - 20 = 0 => (x + 10)(x - 2) = 0 => x = -10 hoặc x = 2 9) x³ + 3x² - 4x - 12 = 0 => (x - 2)(x² + 5x + 6) = 0 => x = 2 hoặc x = -3 hoặc x = -2 10) (x - 3)² + 3 - x = 0 => x² - 6x + 9 + 3 - x = 0 => x² - 7x + 12 = 0 => (x - 3)(x - 4) = 0 => x = 3 hoặc x = 4 11) (x + 3)² - 6x - 18 = 0 => x² + 6x + 9 - 6x - 18 = 0 => x² - 9 = 0 => (x - 3)(x + 3) = 0 => x = 3 hoặc x = -3 12) (x - 2)² - 4x + 8 = 0 => x² - 4x + 4 - 4x + 8 = 0 => x² - 8x + 12 = 0 => (x - 2)(x - 6) = 0 => x = 2 hoặc x = 6 13) (x + 1)(x - 3) + 1 = 0 => x² - 2x - 2 = 0 => x = 1 + √3 hoặc x = 1 - √3 14) (x - 4)² - 4x + 16 = 0 => x² - 8x + 16 - 4x + 16 = 0 => x² - 12x + 32 = 0 => (x - 4)(x - 8) = 0 => x = 4 hoặc x = 8 15) 4x² - 25 + (2x + 5)² = 0 => 4x² - 25 + 4x² + 20x + 25 = 0 => 8x² + 20x = 0 => 4x(x + 5) = 0 => x = 0 hoặc x = -5 16) x² - 1 + (x + 1)(x - 3) = 0 => x² - 1 + x² - 2x - 3x + 3 = 0 => 2x² - 5x + 2 = 0 => (2x - 1)(x - 2) = 0 => x = 1/2 hoặc x = 2 17) x(x + 1) - x² + 1 = 0 => x² + x - x² + 1 = 0 => x + 1 = 0 => x = -1 18) 2x(x - 1) - (1 - x)² = 0 => 2x² - 2x - 1 + 2x² - 2x + 1 = 0 => 4x² - 4x = 0 => 4x(x - 1) = 0 => x = 0 hoặc x = 1 19) x² - 4 + (x + 2)(x - 3) = 0 => x² - 4 + x² - x - 6 = 0 => 2x² - x - 10 = 0 => (2x + 5)(x - 2) = 0 => x = -5/2 hoặc x = 2 20) x² - 1 + (x + 1)(x - 3) = 0 => x² - 1 + x² - 2x - 3x + 3 = 0 => 2x² - 5x + 2 = 0 => (2x - 1)(x - 2) = 0 => x = 1/2 hoặc x = 2