Find the Cartesian equations of the following curves whose parametric equations are :

$x=5\cos \theta ,y=5\sin \theta$

$x=a+c\cos \alpha , y=b+c\sin \alpha$

$x=3\cos \alpha , y=3\sin \alpha$

$x=1+3\cos \theta , y=2-3\sin \theta$

$x=\cos \theta +\sin \theta , y=\sin \theta -\cos \theta$

$x=\frac{20t}{4+t^2}, y=\frac{5\left(4-t^2\right)}{4+t^2}$

$x=5\cos \theta , y=-3+5\sin \theta$,

lies on a circle for all values of $\theta$.