Circle: the right side is r²: the SAT math trap

Short answer: Complete the square first (add 9 and 4 to both sides). Then take the square root.

The trap, in one question

Tempting answer: 12 or √12  (read it off as-is)

Correct answer: 5  ((x − 3)² + (y + 2)² = 25)

How to spot it in 3 seconds

Complete the square first (add 9 and 4 to both sides). Then take the square root.

FAQ

What is the circle: the right side is r2 trap on the SAT?

Example: What is the radius of the circle x2 + y2 − 6x + 4y = 12? The tempting answer is 12 or √12 (read it off as-is); the correct answer is 5 ((x − 3)2 + (y + 2)2 = 25).

How do you avoid the circle: the right side is r2 trap?

Complete the square first (add 9 and 4 to both sides). Then take the square root.

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