D=64-4*12=16
x1=(-8+4)/2=-2
x2=(-8-4)/2-6
<span>производная от 2cosx </span>равна -2sinx
f(x) = (x² - 2x - 3)²
f'(x) = 2(x² - 2x - 3)(2x - 2) = 4(x² - 2x - 3)(x - 1) = 4(x - 3)(x + 1)(x - 1)
f'(x) = 0 => 4(x - 3)(x + 1)(x - 1) = 0
x - 3 = 0 => x = 3
x + 1 = 0 => x = -1
x - 1 = 0 => x = 1
Ответ: x = 3, x = 1, x = -1.