Equation of Ellipse in Reduced Form/Cartesian Frame/Parametric Form

Theorem
The equation of $K$ in parametric form is:
 * $x = a \cos \theta, y = b \sin \theta$

Proof
Let the point $\tuple {x, y}$ satisfy the equations:
 * $x = a \cos \theta$
 * $y = b \sin \theta$

Then: