Question

cos(2x)cosx - sin(2x)sinx = 1

Answer 1

cos2xcosx - sin2xsinx = 1
cos(2x + x) = 1
cos3x = 1
3x = 2pin
x = 2/3pin
Ответ.      2/3pin,  где  n  принадлежит  Z

Answer 2

$cos2xcosx - sin2xsinx = 1 \ cos(2x + x) = cos3x=1 \ 3x = 2pi n \ x = frac{2pi n}{3} , nin Z$