1) x^2 - 18 = 7x
x^2 - 7x - 18 = 0
x^2 + 2x - 9x - 18 = 0
x * (x - 2) - 9 * (x - 2) = 0
(x - 9)(x - 2) = 0
x = -2; 9
Как квадратное уравнение:
x^2 - 18 = 7x
x^2 - 7x - 18 = 0
D = 49 - 4 * (-18) = 49 + 72 = 121
x1 = (7 + 11)/2 = 9
x2 = (7 - 11)/2 = -2
Ответ: 9
2) (-2x + 1)(-2x - 7) = 0
2x - 1 = 0 либо 2x + 7 = 0
x = 1/2 x = -7/2
Ответ: -7/2
3) (x - 6)(4x - 6) = 0
x - 6 = 0 либо 4x - 6 = 0
x = 6 x = 6/4 = 3/2
Ответ: 3/2.
4) (-5x - 3)(2x - 1) = 0
5x + 3 = 0 либо 2x + 1 = 0
x = -3/5 x = -1/2
Ответ: -3/5
5) 5x^2 + 20x = 0
5x * (x + 4) = 0
x=0 либо x = -4
Ответ: -4