Converting $x = \sin \frac{t}{2}, y = \cos \frac{t}{2}$ to Cartesian form How can we transform these parametric equations to Cartesian form? 
$$x = \sin \frac{t}{2}, \quad y = \cos \frac{t}{2}, \quad -\pi \leq t \leq \pi.$$

$$x = \sin \frac{t}{2}, \quad y = \cos \frac{t}{2}, \quad -\pi \leq t \leq \pi.$$
$$x^2+y^2=(\sin \frac{t}{2})^2+(\cos \frac{t}{2})^2=1$$ so
$$x^2+y^2=1$$ is equation of some circle
