Решение простейших тригонометрических уравнений

$$sinx = a, \left | a \right | \leq 1\; \Rightarrow \;\! x=(-1)^{n}arcsin \, a + \pi n, n\subset \mathbb{Z}$$ $$cos\: x = a, \left | a \right | \leq 1\; \Rightarrow \;\! x=\pm arccos \, a + 2 \pi n, n\subset \mathbb{Z}$$ $$tg\: x = a \; \Rightarrow \;\! x=arctg \, a + \pi n, n\subset \mathbb{Z}$$ $$ctg\: x = a \; \Rightarrow \;\! x=arcctg \, a + \pi n, n\subset \mathbb{Z}$$