Вычислите sin30 + cos60 - sin135 * sin135

Решите задачу:

$\sin(30\textdegree) + \cos(60\textdegree) - \sin(135\textdegree) \times \sin(135\textdegree) = \\ = \sin(30\textdegree) + \cos(60\textdegree) - \sin ^{2} (135\textdegree)$

$\sin(30\textdegree) = \frac{1}{2} \\ \cos(60\textdegree) = \frac{1}{2} \\ \sin(135\textdegree) = \sin(90\textdegree+45\textdegree) = \cos(45\textdegree) = \frac{ \sqrt{2} }{2}$

$\frac{1}{2} + \frac{1}{2} - (\frac{ \sqrt{2} }{2} ) ^{2} = 1 - \frac{2}{4} = 1 - \frac{1}{2} = \frac{1}{2}$