Verifying Trigonometric Identities

The process of Verifying Trigonometric Identities is centered around confirming the authenticity of an equation for all possible variable values, utilizing the principles of trigonometry. This typically involves showcasing that two sides of a trigonometric equation are equal, achieved primarily through algebraic adjustments, transformations in trigonometry, and implementing key identities.

Verifying Trigonometric Identities

Verify whether the following is a trig identity: \[ \frac{1}{\sec (\theta)} \circ \tan (\theta)=\sin (\theta) \]

Using Fundamental Identities

Find $\cos (2 A)$, if $\cos (A)=-\frac{21}{29}$, and $A$ is in quadrant 3 . Write in fraction form