A sector perimeter is (3) times its arc length and the radius is (8) cm. What is the central angle?
Answer and explanation
Correct answer: \(1\) radian
The perimeter of a sector is \(2r+s\), where \(s\) is the arc length. From the condition, \(2r+s=3s\). Thus, \(2r=2s\), so \(s=r=8\) cm. Using \(s=r\theta\), we get \(\theta=\frac{s}{r}=\frac{8}{8}=1\) radian. At \(2\) radians, the arc length would be \(16\) cm, so the perimeter would not be three times the arc length. Exam tip: Use \(s=r\theta\) only when \(\theta\) is measured in radians.
Frequently asked questions
What is the correct answer to this question?
\(1\) radian
Why is this the correct answer?
The perimeter of a sector is \(2r+s\), where \(s\) is the arc length. From the condition, \(2r+s=3s\). Thus, \(2r=2s\), so \(s=r=8\) cm. Using \(s=r\theta\), we get \(\theta=\frac{s}{r}=\frac{8}{8}=1\) radian. At \(2\) radians, the arc length would be \(16\) cm, so the perimeter would not be three times the arc length. Exam tip: Use \(s=r\theta\) only when \(\theta\) is measured in radians.
Which subject and chapter does this question cover?
This is a Class 12 Mathematics question. Chapter: Trigonometric Functions. Topic: Angles.
