ACT · Coordinate Geometry · Circles in the coordinate plane
Question act-q-00434
Easy Multiple choice No calculator
The question
A circle has radius 4. What is its area, in terms of π?
- 32π
- 16π
- 4π
- 8π
Show answer & worked solution
Answer: 16π
Worked solution. Area of a circle is πr². Here r = 4, so area = π × 4² = 16π.
Why each wrong choice is wrong. Confusing area (πr²) with circumference (2πr) is the dominant error here. The 2πr distractor catches it perfectly.
Test-day tactic. Area scales as the square of the radius; circumference scales linearly. When in doubt, sketch a unit circle and check.
About this question type
Items test the standard form (x − h)² + (y − k)² = r² and conversions to and from general form by completing the square.
You will see a question shaped like this one on roughly every other official ACT form, typically at an early position in the section, where missing them carries an outsize penalty because the curve assumes everyone in your band gets them right. Treat any miss in this subtopic as a signal to drill the subtopic page before you do another full practice test.