The negative coterminal angle of an angle between \(-2\pi\) and (0) is \(-\frac{7\pi}{18}\). What is its principal positive angle?
Answer and explanation
Correct answer: \(\frac{29\pi}{18}\)
Coterminal angles differ by an integral multiple of \(2\pi\). Add \(2\pi\) to the given negative angle: \(-\frac{7\pi}{18}+2\pi=-\frac{7\pi}{18}+\frac{36\pi}{18}=\frac{29\pi}{18}\). This value lies between \(0\) and \(2\pi\), so it is the principal positive angle. The difference between \(\frac{25\pi}{18}\) and \(-\frac{7\pi}{18}\) is \(\frac{16\pi}{9}\), which is not an integral multiple of \(2\pi\). Exam tip: to convert a negative angle into its principal positive form, add \(2\pi\) as needed.
Frequently asked questions
What is the correct answer to this question?
\(\frac{29\pi}{18}\)
Why is this the correct answer?
Coterminal angles differ by an integral multiple of \(2\pi\). Add \(2\pi\) to the given negative angle: \(-\frac{7\pi}{18}+2\pi=-\frac{7\pi}{18}+\frac{36\pi}{18}=\frac{29\pi}{18}\). This value lies between \(0\) and \(2\pi\), so it is the principal positive angle. The difference between \(\frac{25\pi}{18}\) and \(-\frac{7\pi}{18}\) is \(\frac{16\pi}{9}\), which is not an integral multiple of \(2\pi\). Exam tip: to convert a negative angle into its principal positive form, add \(2\pi\) as needed.
Which subject and chapter does this question cover?
This is a Class 12 Mathematics question. Chapter: Trigonometric Functions. Topic: Angles.
