## Trigonometry (11th Edition) Clone

$$\cot\frac{A}{2}=\frac{1+\cos A}{\sin A}$$
$$\tan\frac{A}{2}=\frac{\sin A}{1+\cos A}$$ - From Reciprocal Identities, we have: $$\cot\theta=\frac{1}{\tan\theta}$$ Therefore, we can apply the identity for angle $\frac{A}{2}$ in place of $\theta$. $$\cot\frac{A}{2}=\frac{1}{\tan\frac{A}{2}}$$ Thus, $$\cot\frac{A}{2}=\frac{1}{\frac{\sin A}{1+\cos A}}$$ $$\cot\frac{A}{2}=\frac{1+\cos A}{\sin A}$$ That is the identity for $\cos\frac{A}{2}$.