$$ \dfrac{dy}{dx}=\dfrac{\sin \left( a+y \right)}{\cos y-x.\cos \left( a+y \right)} $$
Find $$ \dfrac{{dy}}{{dx}},x = a\left( {\cos t + \log \tan \frac{t}{2}}
\right),y = a\sin t$$
If $$\sin y = x \sin (a + y)$$, then prove that $$\dfrac{dy}{dx} = \dfrac{\sin^2 (a+y)}{\sin a}$$.