\(2\left(sin^6x+cos^6x\right)+1=2\left(sin^2x+cos^2x\right)^3-6sin^2x.cos^2x\left(sin^2x+cos^2x\right)+1\)
\(=3-6sin^2x.cos^2x\) (1)
\(3\left(sin^4x+cos^4x\right)=3\left(sin^2x+cos^2x\right)^2-6sin^2x.cos^2x\)
\(=3-6sin^2x.cos^2x\) (2)
(1);(2) \(\Rightarrow\) đpcm