(4/9)^cosx+2(2/3)^cosx-3=0

[latex]( frac{4}{9} )^{cosx}+2( frac{2}{3}) ^{cosx}-3=0 \ (frac{2}{3})^{cosx}=t, = extgreater t extgreater 0 \ t^2+2t-3=0 \ t_1=1, t_2=-3 = extgreater t=1 \ ( frac{2}{3}) ^{cosx}=1 \ cos x=0 \ x= frac{ pi }{2} + pi k, k in Z[/latex]