Name Date Circles and Parabolas ANSWER KEY 4.1 Circles A. Writing the equation of a circle 1. Write the standard form of a circle with center C(h,k) & radius r: 2. If you solve this equation for r, write the new equation: Write the equation of the circle: a. C(2,-5), radius 2 b. C(-2,-5) radius 4 c. C(-2,5) , radius 3 d. C(2,-5) radius 5 B. Rewriting an Equation of a Circle to Graph the Circle 4. Fill in the blanks: In order to graph an equation of a circle that is expanded in the form ax2+ ay2 + cx + dy + e = 0, you must on both and to in form and identify the circle's and 5. Study examples 2 A & B on page 117 then complete the following problems: Write each circle in standard form, then identify the center and the radius: a. x2 + y2 + 4x +12y + 39 =0 Equation : Center ( _) radius Show work below: b. 2 x2 + 2y2 + 20x +12y + 50 =0 Equation : Center ( ) radius Show work below: 10