Question

Решите пожалуйста
cos2x = 2cosx - 1

Answer 1

$cos2x=2cosx-1 \ 2cos^{2}x-1-2cosx+1=0 \ 2(cos^{2}x-cosx)=0 \ cosx=0 \ x=pi /2+pi n \ cosx=1 \ x=2pi n$