Cos2 A + tan2 A – sec2 A ekuivalen dengan ..

[tex]\displaystyle \cos^2a+\tan^2a-\sec^2a=\cos^2a+\frac{\sin^2a}{\cos^2a}-\frac{1}{\cos^2a}\\\cos^2a+\tan^2a-\sec^2a=\cos^2a+\frac{\sin^2a-1}{\cos^2a}\\\cos^2a+\tan^2a-\sec^2a=\cos^2a+\frac{\cos^2a}{\cos^2a}\\\boxed{\boxed{\cos^2a+\tan^2a-\sec^2a=\cos^2a+1}}[/tex]