The standard equation for a circle is (x-h)2 + (y-k)2 = r2, where (h,k) represents the center of the circle and r represents the radius. When solving for the center or radius, the terms in the parentheses change signs - the x and y terms change to the opposite of the center coordinates h and k, and the radius r is the square root of the number after the equals sign.

1. Terms of Endearment
Equations of Circles: 10.6

2. Standard Equation for a Circle
• (x-h)2 + (y-k)2 = r2
• How do I work it…
• Just like when you solve factoring
problems, what is in the ( ) always
changes signs…the sooner you
learn this the easier Algebra II will
be.
• The center is the opposite sign of
what is with the x and the y
• The radius is the square root of the
number after the equals sign