4sin^2 3x cos^2 3x + 8sin^2 3x=0

4sin^2x(cos^2 3x+2)=0

4sin^2 3x=0 

sin^2 3x=0

1-cos6x/2=0

cos6x=1

6x=2pn

x=pn/3

sin^2 2x+cos4x=0

sin^2x+cos^2 2x-sin^2 2x=0

cos^2 2x=0

1+cos4x/2=0

cos4x=-1

4x=p+2pk

x=p/4+pk/2