[tex]cos^22x-8cos2x.sin2x+3sin^22x=3[/tex] xets cos2x=0 => 3sin^2(2x)=3=>sin^2(2x)=1 => nghiem x=..... xet cos2x khac 0 => [tex]1-\frac{8sin2x}{cos2x}+\frac{3sin^22x}{cos^22x}=1-8tan2x+3tan^22x=3[/tex] =>
