Which angle is coterminal with \(\frac{5\pi}{8}\) and lies between \(-4\pi\) and \(-2\pi\)?
Answer and explanation
Correct answer: \(-\frac{27\pi}{8}\)
Coterminal angles differ by an integer multiple of \(2\pi\). Subtracting \(4\pi=\frac{32\pi}{8}\) from \(\frac{5\pi}{8}\) gives \(\frac{5\pi}{8}-\frac{32\pi}{8}=-\frac{27\pi}{8}\). Moreover, \(-4\pi=-\frac{32\pi}{8}< -\frac{27\pi}{8}< -\frac{16\pi}{8}=-2\pi\), so option D lies in the required interval. Option A differs from \(\frac{5\pi}{8}\) by \(-3\pi\), which is not an integer multiple of \(2\pi\). Exam tip: write coterminal angles as \(\theta+2n\pi\) and then test the required interval.
Frequently asked questions
What is the correct answer to this question?
\(-\frac{27\pi}{8}\)
Why is this the correct answer?
Coterminal angles differ by an integer multiple of \(2\pi\). Subtracting \(4\pi=\frac{32\pi}{8}\) from \(\frac{5\pi}{8}\) gives \(\frac{5\pi}{8}-\frac{32\pi}{8}=-\frac{27\pi}{8}\). Moreover, \(-4\pi=-\frac{32\pi}{8}< -\frac{27\pi}{8}< -\frac{16\pi}{8}=-2\pi\), so option D lies in the required interval. Option A differs from \(\frac{5\pi}{8}\) by \(-3\pi\), which is not an integer multiple of \(2\pi\). Exam tip: write coterminal angles as \(\theta+2n\pi\) and then test the required interval.
Which subject and chapter does this question cover?
This is a Class 12 Mathematics question. Chapter: Trigonometric Functions. Topic: Angles.
