How to answer it
- Match the equation to (x − h)² + (y − k)² = r².
- Flip the signs inside the parentheses to get the center.
- Take the square root of the right side for the radius.
Worked example
An original question in the SAT format, already answered.
SAT MathWorked example
(x − 2)² + (y + 3)² = 49
What are the center and radius of the circle?
- ACenter (2, −3), radius 7
- BCenter (−2, 3), radius 7
- CCenter (2, −3), radius 49
- DCenter (−2, 3), radius 49
Answer: A. y + 3 is y − (−3), so the center is (2, −3). The right side is r², so r = √49 = 7.
The most common trap
Using 49 as the radius. The equation gives the radius squared.
Practice it
Hourly Prep’s daily sets mix circles with the rest of SAT Math, and send more of it your way when it’s a weak spot. See how the SAT prep plan works, or browse the other SAT skill guides.