Work with circles (arcs, chords, tangents, central/inscribed angles) and circle equations when presented.
Circle questions usually come down to arc, radius, or standard-form relationships.
Core Idea
In circle problems, connect everything to the intercepted arc or a radius fact: a central angle equals its arc, an inscribed angle is half its intercepted arc, and a tangent is perpendicular to the radius at the point of tangency.
Understanding
Rule: Circle questions become simpler when you ask what arc or radius relationship controls the picture. Central angles match their arcs directly. Inscribed angles are half the intercepted arc. Equal chords subtend equal arcs, and tangent segments create right angles with radii at the point of tangency.
If ACT gives a circle equation, standard form lets you read the center and radius directly instead of expanding anything.
Worked Example
A central angle intercepting arc
Select an answer to see the explanation