Question 136921
Hi,

The given equation is {{{X^2/4 + y^2/4=1}}}

Now taking the common denominator as 4,
multiply both sides by the common denominator.
==> x^2 + y^2 = 4

This can be compared with the standard equation of the circle which is 
x^2 + y^2 = r^2

==> the radius = 2
and the centre is the origin (0,0)

Thus the centre is (0,0) and the radius is 2 units

Good luck!!!

dolly