12.1 Circles
Unit 12 · Conic sections
Ideas in this lesson
Centers and radii
In standard circle form, subtract the center coordinates before squaring; the right side is the radius squared.
Write a circle equation
Use a center and a point to find the squared distance, then substitute it for the radius squared.
Complete the square
Group coordinate terms and add the square-completing constants to both sides.
Line-circle intersections
Substitute the line equation into the circle and solve; zero, one or two real intersections may result.
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