Finding arc length
Arc length is the angle's fraction of 360° times the circumference.
The common mistake
Using the area formula πr² instead of the circumference.
Instead: Arc length = (θ/360) × 2πr.
Worked example with Guide me
Find the arc length for a 90° angle in a circle of radius 8.
- Sugar · What fraction of the circle is 90°?Student · ¼.
- Sugar · Full circumference?Student · 16π.
- Sugar · A quarter of that?Student · 4π.
Answer: 4π ≈ 12.6
Try 3 practice questions
1. 180°, radius 5?
Show answer
5π ≈ 15.7
2. 60°, radius 6?
Show answer
2π ≈ 6.3
3. 120°, radius 9?
Show answer
6π ≈ 18.8
Quick answers
- What is the most common mistake with finding arc length?
- Using the area formula πr² instead of the circumference.
- How do I get finding arc length right?
- Arc length = (θ/360) × 2πr.
- Can you show a worked example?
- Find the arc length for a 90° angle in a circle of radius 8. 4π ≈ 12.6
Related concepts
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