Помогите с алгеброй, пожалуйстааа

$\sqrt{x - 1 + \sqrt{x + 2 } } = 3 \\ \\ x - 1 + \sqrt{x + 2 } = 9 \\ \\ \sqrt{x + 2 } = 10 - x \ \ \ \ \ \ \ \boxed{x \leq 10} \\ \\ x + 2 = 100 - 20x + x^2 \\ \\ x^2 - 21x + 98 = 0 \\ \\ x^2 - 14x - 7x + 98 = 0 \\ \\ x(x - 14) - 7(x - 14) = 0 \\ \\ (x - 7)(x - 14) = 0 \\ \\ x = 7; \ x = 10 - \ postoronniy \ \ koren \\ \\ \boxed{OTBET: \ x = 7. }$

sin2xsinx - cos2xcosx ≤ 1/2
cos2xcosx - sin2xsinx ≥ -1/2
По формуле косинуса суммы аргументов:
cos(2x + x) ≥ -1/2
cos3x ≥ -1/2
-2π/3 + 2πn ≤ 3x ≤ 2π/3 + 2πn, n ∈ Z
-2π/9+ 2πn/3 ≤ x ≤ 2π/9 + 2πn/3, n ∈ Z