You know from the text that the graph of the equation x 2 + y 2 = 9 is...

You know from the text that the graph of the equation x ² + y ² = 9 is a circle with center (0, 0) and radius 3. In Exercises 75–81, use a graphing utility to investigate what happens when the equation is changed slightly. (As in graphing circles, you’ll first need to solve the given equations for y.)