# Circle Equation: Center NOT (0,0)

- Author:
- Emily Reed, Tim Brzezinski

- Topic:
- Circle

Experiment with the interactive visualization below and answer the questions that appear below the applet.

*Note: To drag with circle without changing its radius, simply drag the circle itself (and not the points on the circle).***Questions:**1) Suppose

*P(x,y)*= any point that lies on a circle with center (3, 4) and radius 4. Use what you've observed to write an equation that expresses the relationship among

*x*,

*y*, and

*r*. (No need to square any binomial expressions.) 2) What is the equation of a circle with center (-1, 5) and radius

*r*= 9? (No need to square any binomial expressions.) 3) Suppose another circle has center (-2, -8). Suppose this circle also passes through the point (4, 0). Write the equation of this circle. (Again, don't square any binomial expressions.) (HINT: How can we find the radius using our given information?)