Question

cos(fi)=2cos(fi)
Найти fi

Answer 1

fi=X

$\cos(x) = 2 \cos(x) \\ \cos(x) - 2 \cos(x) = 0 \\ - \cos(x) = 0 \\ \cos(x) = 0 \\ \\ fi = \frac{\pi}{2} + k\pi$