Question

Помогите с алгеброй
Даю 40 баллов​

Answer 1

$-1\leq \cos{x}\leq 1; \\ \\ \cos{x}-1\geq 0 \\ \\ \cos{x}\geq 1 \\ \\ \left \{ {{-1\leq \cos{x}\leq 1} \atop {\cos{x}\geq 1}} \right. \ \ \ \ \ => \ \ \ \cos{x}=1 \\ \\ x=2\pi n, n \in Z$