What you’ll learn
Graph circles.
Key idea
Radius is a center-to-boundary displacement, not an absolute coordinate or the full diameter.
Radius is displacement from center, not absolute coordinate; include every cardinal endpoint.
Worked example
Enter the exact value or ordered values in the format requested below.
O is the circle center; R,L,U,D are its cardinal boundary points on this grid. Find its radius in coordinate units; x horizontal, y vertical.
Labeled coordinates: O=(-3, 1); R=(2, 1); L=(-8, 1); U=(-3, 6); D=(-3, -4).
- O=(-3,1), R=(2,1); their horizontal distance is 2-(-3)=5.
- That is the radius; the full diameter would be 10.
Answer: 5
Quick Check
Relate the graph used in 'Graph circles' to an equation, table, transformation, or verbal description.
Connect the plotted circle center O and cardinal points R,L,U,D to its full equation with geometric justification; x horizontal, y vertical.
Labeled coordinates: O=(-2, 2); R=(0, 2); L=(-4, 2); U=(-2, 4); D=(-2, 0).