Equation for simple parametric curve

Question

My math skills are rusty. I want to find the parametric equation for the 5 vertices curve below. It consists of an ellipse with a rotating axes. I get stuck after this:

$$x = a \cos(t) \cos(\theta) - b \sin(t) \sin(\theta)$$

$$y = a \cos(t) \sin(\theta) + b \sin(t) \cos(\theta)$$

with $\theta = function (t)$?

Answer 1

$x(t) = 6\cos(t-{\pi\over2})\cos({t\over5})-\sin(t-{\pi\over2})\sin({t\over5})$

$y(t) = 6\cos(t-{\pi\over2})\sin({t\over5})+\sin(t-{\pi\over2})\cos({t\over5})$

with $0<t<5\pi$