Circles on the Digital SAT: the Desmos Method
A circle equation is a sentence that says where the middle is and how far it is to the edge. Once you can read those two things, every circle question on the SAT is either reading them straight off, or building them from two points.
Geometry & Trigonometry·65 practice problems in DesPrep
The Circles lesson is part of DesPrep
It is one of the 17 full lessons inside the subscription — 7 sections that take circles from first principles to the fastest Desmos route, with a worked example on every one:
- The equation already tells you where the circle is
- The number on the right is r squared, not r
- Two ends of a diameter: the center is halfway between
- A radius is a distance, so it is a right triangle
- The semicircle: how to get a point you can actually click
- General form: the ugly ones, and why they are not
- Tangents and arcs: the two that need no graph
Then 65 practice problems on this skill alone, solved inside a live Desmos calculator with step feedback and an expert replay on every one.
More Geometry & Trigonometry guides
- Area and VolumeArea and volume formulas evaluated in Desmos, including the maximum-area problems that are really parabolas in disguise.
- Lines, Angles and TrianglesAngle relationships and triangle facts, with Desmos handling the arithmetic.
- Right Triangles and TrigonometryPythagorean triples and the three ratios, kept exact as fractions.