Next, to see this equation on a calculator, we actually have to use two separate functions. This is because a circle is not a function — think back to the Vertical Line Test.
y=sqrt(9-x^2) and y=- sqrt(9-x^2)
To enter these functions, push Y= and type them in two different rows. Then push GRAPH to draw them.
Looking at the graph, we can see that the circle has a radius of 3. Also, both of its x- and y-intercepts occur at 3 and -3.
