Решил 4 и 5 номер.
6cos^2x+4cos^3x-3cosx=cosx
6cos^2x+4cos^3x-4cosx=0
2cosx(3cosx+2cos^2x-2)=0
cosx=0 x=П/2(2k+1)
2cos^2x+3cosx-2=0 cosx=t t<=|1|<br>2t^2+3t-2=0
t=(-3+-5)/4 t=1/2
cosx=1/2 x=+-П/3+2Пk
5.sin^2x(sinx+cosx)+cos^2x(sinx+cosx)=cos2x
(sinx+cosx)=cos2x
tgx=-1
tgx=1
x=+-П/4+Пk