Lesson 4 1 Circles Standard Form of a

Lesson 4 -1 Circles

Standard Form of a Circle • (h, k) is the center of the circle • The radius of the circle is r • When plugging h and k into the equation they will change signs since is subtraction in the standard form of a cirlce

Example • Write the equation of a circle with a center at (-3, 2) and radius of 4

Example • Write the equation of a circle with a center at (1, -4) and a radius of 2

You Try • Write the equation of a circle with a center at (4, -11) and a radius of 16

Graphing a circle from standard form • Find the center of the circle (h, k) (remember to change signs when pulling them from the equation) • Plot the center of the circle • Find the radius of the circle (square root of r^2 in the equation) • Go left, right, up, and down r units from the center and put at each • Draw your best circle through the four points from step 4

Example

Example

You Try

Writing an equation from a graph • Find h and k which is the center of the circle • Count from the center of the circle to the outside (this is your radius) • Plug h, k, and r into your standard form for a circle

Example

Example

You Try

Finding the center and radius from the standard form equation • Pull out h and k remember to change signs this is your center (h, k) • Find r ( take the square root of the answer)

Example • Find the center and the radius of the circle

You try • Find the center and radius of the circle

Homework • Circle worksheet • Work all the problems