cos(x-П/9)cos(3х+6П/5)=0

cos(x-Pi/9)=0
X-Pi/9=Pi/2+Pi*n, n=1,2,3...
X1=pi/2+pi/9+pi*n
X1=(9Pi+2Pi)/9+pi*n
X1=11pi/9+pi*n

Или

3x+6pi/5=pi/2+pi*n, n=1,2,3,...
3X2=pi/2-6pi/5+pi*n
3X2=(5pi-12pi)/10+pi*n
X2=-7pi/30+pi*n/3