## Trigonometry (11th Edition) Clone

$$(1+\tan\theta)^2-2\tan\theta=\sec^2\theta$$
$$A=(1+\tan\theta)^2-2\tan\theta$$ $$A=(1+\tan^2\theta+2\tan\theta)-2\tan\theta$$ $$A=1+\tan^2\theta+2\tan\theta-2\tan\theta$$ $$A=1+\tan^2\theta$$ We know from a Pythagorean Identity that $$1+\tan^2\theta=\sec^2\theta$$ That means $$A=\sec^2\theta$$