Question

21 номер, пожалуйста

Answer 1

$\ frac{-18}{x^2 - 4x - 21} leq 0 \ \ x^2 - 4x - 21 = 0 \ \ D = (-4)^2 - 4*(-21) = 16 + 84 = 100 \ \ sqrt{100}=10$
$\ x_1 = frac{4+10}{2} = frac{14}{2} = 7 \ \ x_2 = frac{4-10}{2} = -3$
$\ x^2 - 4x - 21 = (x-7)(x+3) \ \ frac{18}{(x-7)(x+3)} leq 0 \ \ - 18(x-7)(x+3) leq 0 \ \ (x-7)(x+3) geq 0\ \x_1 = 7 \ x_2 = -3$
____+______-3____________-____________7___________+________
x∈(-∞;-3) U (7 ; + ∞)