Question

решите уравнеие: cos7x+cosx=0

Answer 1

$cos 7x+cos x=0 \ 2cos frac{7x+x}{2} cdot cos frac{7x-x}{2} =0 \ 2cos4xcdot cos 3x=0 \ left[begin{array}{ccc}cos 4x=0\ cos 3x=0end{array}rightto left[begin{array}{ccc}x_1= frac{pi}{8} + frac{pi n}{4}, n in Z\ x_2=frac{pi}{6} + frac{pi n}{3}, n in Z end{array}right$