Cartesian Co-ords are the the one on the (x,y) graphs that you regularly work with.
Where polar Co-ords where each point is referenced from a fixed point and a angle (r, )
So to convert between them there is a formula.
So with 2a
your answer would be (2cos( ),2sin ( ))
I Used tan because I personally find it easier to visualise in my head. the co-ord is 2 along the x and 2 along the y direction.
Also you can simply convert the 45 degrees to radians if needed.
2 c,d I have never seen those before So I'll let someone more experienced to help there.