1. 9.3 Graph & Write Equations of Circles Algebra 2

2. Standard Form of the Equation of a circle (center at origin) with radius, r

3. Ex. 1) Graphing an Equation of a Circle  Draw the circle

4. Ex. 2) Graphing an Equation of a Circle  Draw the circle

5. Ex. 3 Write the standard form of the equation of the circle with the given radius & whose center is the origin.

6. Distance formula/radius when center is (0,0)

7. Ex. 4) Write an Equation of a Circle  when (-4,7) is on a circle centered at the origin.

8. To find a tangent line  1.) Find the slope of the radius  2.) Find Slope – opp. Reciprocal for a perp. Line to the radius  3.) Use given point & new slope from step #2 to plug into point- slope form or slope intercept form (twice).  4.) Final equation should be in slope intercept form.

9. Ex. 5) Finding a Tangent Line  Write an equation of the line that is tangent to the circle

10. Using circles in real life  Region inside circle:  Region outside circle:

11. Ex. 6  A street light can be seen on the ground within 30 yd of its center. You are driving and are 10 yd east and 25 yd south of the light. a.) Write an inequality to describe the region on the ground that is lit by the light. b.) Is the street light visible?