SAT Circles Guide: Every Formula and Trap
How to solve every SAT circle question, from basic circumference to standard-form equations with a completing-the-square step.
The Circle Equation
The standard form of a circle is (x − h)² + (y − k)² = r², where (h, k) is the center and r is the radius.
Completing the Square
When the SAT gives you a circle equation in expanded form, you'll need to complete the square on both the x and y terms to rewrite it in standard form. Then the center and radius fall out.
Arcs and Sectors
Arc length = (θ/360) × 2πr for degrees, or θ × r for radians. Sector area = (θ/360) × πr² for degrees, or (θ/2) × r² for radians.
What to do after reading this
- Turn the article into one action: a bank drill, a timed module, or a score calculation.
- Write down the exact skill or habit you are testing.
- Review the result before reading another guide.
Related SAT guides
- SAT Geometry Overview: Every Topic Tested
The Digital SAT tests geometry lightly but predictably. Here's the full topic list with what matters for each.
- Every SAT Math Formula You Need to Memorize
The complete list of Digital SAT math formulas to memorize — including what the reference sheet already covers and what it doesn't.
Mistakes to avoid
- Reading multiple guides without doing practice between them.
- Using broad practice when the article points to a narrow skill.
- Treating format knowledge as score improvement before testing it under time.
Use this in practice
Practice on 1600.now
Apply what you just read. Run the numbers in the SAT score calculator, take a full Digital SAT module, or drill targeted skills in the question bank.
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