Question

Show that ${\tan }^2\theta -\frac{1}{{\cos }^2\theta }=-1$.

Answer 1

Formula used:
$se{c}^2\theta -ta{n}^2\theta =1$
$ta{n}^2\theta -\frac{1}{co{s}^2\theta }=ta{n}^2\theta -se{c}^2\theta$
$=-(se{c}^2\theta -ta{n}^2\theta )$
$=-1$