sinΘ+sin^{2}Θ=1 then cos^{2}Θ+ cos^{4}Θ=?
sin(x)+sin^{2}(x)=1
sin^{2}(x)+cos^{2}(x)=1 is a trig identity
sin(x)+sin^{2}(x)=sin^{2}(x)+cos^{2}(x)
sin(x)=cos^{2}(x)
Looking at cos^{2}(x)+cos^{4}(x) we have:
sin(x)+[cos^{2}(x)]^{2}
sin(x)+[sin(x)]^{2}
sin(x)+sin^{2}(x) which equals 1 from your hypothesis above
Therefore cos^{2}(x)+cos^{4}(x)=1 also