Circle Equation
Centre and radius from an equation by completing the square, or the equation from a centre and radius, a diameter or three points. Check points and find tangents.
A
B
A and B are the ends of a diameter (x then y).
P₁
P₂
P₃
Three points on the circle (x then y).
Check a point (inside, on or outside, and the tangent)
P
Leave empty to skip.
Fractions and decimals work. For a radius like √13, type \sqrt then the number (or use the √ key on the touchscreen keyboard).