Question

Найти 3cos²ɸ, если ɸ=arccos 1/2√3

Answer 1

$3\cos^2\phi=3\cos^2(\arccos \frac{1}{2\sqrt{3}})=3\cdot \left(\frac{1}{2\sqrt{3}}\right)^2=3\cdot \frac{1}{4\cdot 3}=\frac{1}{4}$