Circle Properties
Work with radius, diameter, circumference, area, arcs, and sectors.
Practice Problems
r=6, θ=60°
Central angle 80°, inscribed angle?
Pro Tips & Shortcuts
SAT Tip: All radii of the same circle are equal length.
SAT Tip: Central angle and its arc have the same degree measure.
SAT Tip: The fraction θ/360° tells you what portion of the circle you have.
SAT Tip: 60° is 1/6 of 360°, so the arc is 1/6 of the circumference.
SAT Tip: This is a key circle theorem: inscribed angle is half the central angle.
If you know diameter, divide by 2 to get radius. If you know radius, multiply by 2 for diameter.
For arc length or sector area, use the fraction (angle/360°) times the whole.
A 90° angle is 1/4 of the circle, so arc and sector are 1/4 of total.
Simplify the fraction first: 60/360 = 1/6.
Any angle inscribed in a semicircle is a right angle (90°).