just realli confused with parameterss especially with trig equations

a) x = 2costheta y=2sintheta 0<theta<pi

Mr F says: Square each of them and then add together.
b) x=cos t, y=cos t 0< t < 2pi

Mr F says: Square each of them and then add together.
c) x=2cos theta, y = root 3 sin theta 0<theta<2pi

Mr F says: and . Square each of these and then add together.
d) x = 2 cos t, y = sin t , 0< theta < pi

Mr F says: and . Square each of these and then add together.
e) 2t/[(1+t)squared], y = [(1-t)squared]/[(1+t)squared]

i have the answers to these questions i jst dont haf the solution and i dont no how to get there

im also realli confused about the restrictions

any help is GREATLY appreciated

thankyouu !