Choose the circle value you know, solve the rest, and use the specialist circle-equation or arc/sector tools when coordinates or angles are part of the problem.
Keep linear inputs in a consistent unit, verify that side lengths or coordinate points can form the stated shape, and treat sketches as explanatory unless explicitly marked to scale. Coordinate formulas can become unstable for nearly degenerate shapes, so invalid or nearly collinear inputs are rejected rather than silently returning misleading values.
Use the tool first, then apply these checks to verify the inputs, interpret the result, and hand it off without displacing the primary workflow.
Radius, diameter, circumference, and area are related, but they are not interchangeable input observations. Select the quantity that was measured or specified rather than converting a rounded secondary value back into the circle and compounding rounding error.
Radius, diameter, and circumference use linear units; area uses squared units. Convert the known measurement before calculation when unit systems differ, and label the result explicitly so a copied area value is not later interpreted as a length.
After solving for radius, diameter should equal twice the radius and circumference divided by pi should equal the diameter. Area divided by pi should equal radius squared. These quick checks can expose a wrong input type or unit before the result is reused.
A whole-circle calculator does not need to absorb every chord, arc, sector, tangent, and segment workflow. When the problem includes a central angle or partial circumference, move to the appropriate specialist so the extra geometry and angle units remain explicit.
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