Корень из 300 cos квадрат х 13П/12-корень из 75

Решите задачу:

$\sqrt{300}cos^2\frac{13\pi}{12}-\sqrt{75}=\sqrt{75}(\sqrt{4}*cos^2\frac{13\pi}{12}-1)=\sqrt{75}(2*cos^2\frac{13\pi}{12}-1)\\=\sqrt{75}*cos(2*\frac{13\pi}{12})=\sqrt{75}*cos\frac{13\pi}6=\sqrt{75}*cos(\frac{13\pi}6-2\pi)=\\=\sqrt{75}*cos(\frac{13\pi}6-\frac{12\pi}6)=\sqrt{75}*cos\frac{\pi}6=\sqrt{75}*\frac{\sqrt3}2=\frac{\sqrt{225}}2=\frac{15}2=7,5$