Question 681672
x^2 + y^2 = 1


can be rewritten as 


(x-0)^2 + (y-0)^2 = 1^2


and that is in the form 


(x-h)^2+(y-k)^2=r^2, which is a circle with radius r and center (h,k)


Since h = 0, k = 0 and r = 1, the center of x^2 + y^2 = 1 is (0,0) and it has a radius of 1 unit. This is a special circle known as the unit circle (which you'll use a lot in trigonometry).


The graph looks like this


{{{ drawing(500, 500, -5, 5, -5, 5,
 graph( 500, 500, -5, 5, -5, 5,0),
 circle(0,0,1)

)}}}