SAT Circles Questions
Radius, arcs, sectors, angles, and the equation of a circle.
In short
- Circles is part of Geometry and Trigonometry, about 15% of the scored Math questions: 5 to 7 on every test.
- Math questions from all four areas are mixed in each module and arranged from easiest to hardest.
- Circumference vs. area is the trap Rivie's practice tests set most often in Circles questions.
Common traps
Most common first, from Rivie's ten practice tests.
Circumference vs. area
Mixing 2πr (circumference) with πr² (area): the wrong choice uses the formula for the other quantity.
The usual mistake: You memorize both formulas and grab whichever you saw most recently. The trap distractor uses the other.
Chord distance bisector
A perpendicular from a circle's center to a chord bisects the chord; the wrong choice ignores this and treats the perpendicular leg as the full chord.
The usual mistake: You set up the right triangle correctly but use the whole chord length where you needed half of it.
Arc fraction of circumference
Arc length = (central angle / 360°) × 2πr. The wrong choice forgets to multiply by 2πr, or accidentally applies the area-of-sector formula instead.
The usual mistake: You set up the angle ratio but apply it to the wrong base (radius, area, or diameter) instead of the full circumference. Length always pairs with circumference.
Try a question
From Rivie's practice tests. Pick an answer to see why it is right or wrong.
In a circle, a chord of length 24 is located 5 units from the center of the circle. What is the length of the radius of the circle?
Video lessons
Free on YouTube, picked for this topic.