Question

cosx+cos5x=0???как решить??

Answer 1

$cosx + cos 5x = 0\ 2cos3x cdot cos(-2x) = 0\ <=> begin{cases} cos3x = 0\cos2x = 0 end{cases} begin{cases} 3x = +- frac{pi}{2} + 2pi n\2x = +- frac{pi}{2} + 2pi kend{cases}\ begin{cases} x = +-frac{pi}{6} + frac{2pi}{3}n\x = +-frac{pi}{4} + pi kend{cases}$