Question 163644
{{{x^2+y^2=36}}}
{{{y^2=36-x^2}}}
{{{y=0+-sqrt(36-x^2)}}}
Then choose x values between (-6,6) and get the y values. 
X values have to be in that interval for the square root function to make sense.
(-6,0)
(0,6)
(0,-6)
(6,0)
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{{{ graph( 300, 300, -7, 7, -7, 7, -sqrt(36-x^2),sqrt(36-x^2)))}}}
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The equation is for a circle centered at (0,0) with a radius of 6.
The positive square root gives the top (positive) portion of the graph, the negative square root, the bottom portion of the graph.