In Exercises 35–60, find the reference angle for each angle. -13𝜋/3
Ch. 1 - Angles and the Trigonometric Functions

Chapter 1, Problem 1.1.64
In Exercises 57–70, find a positive angle less than or that is coterminal with the given angle. 17𝜋 /5
Verified step by step guidance1
Understand that two angles are coterminal if they differ by an integer multiple of \(2\pi\). This means we can add or subtract \(2\pi\) to the given angle to find coterminal angles.
Given the angle \(\frac{17\pi}{5}\), we want to find a positive angle \(\theta\) such that \(0 \leq \theta < 2\pi\) and \(\theta\) is coterminal with \(\frac{17\pi}{5}\).
To do this, subtract multiples of \(2\pi\) from \(\frac{17\pi}{5}\) until the result lies between \(0\) and \(2\pi\). Express \(2\pi\) with denominator 5 as \(\frac{10\pi}{5}\) for easier subtraction.
Calculate \(\frac{17\pi}{5} - 2\pi = \frac{17\pi}{5} - \frac{10\pi}{5} = \frac{7\pi}{5}\). Since \(\frac{7\pi}{5}\) is positive and less than \(2\pi\), this is the coterminal angle you are looking for.
Verify that \(0 \leq \frac{7\pi}{5} < 2\pi\) to confirm the angle is within the desired range.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Coterminal Angles
Coterminal angles are angles that share the same initial and terminal sides but differ by full rotations of 2π radians. To find a coterminal angle, you add or subtract multiples of 2π until the angle lies within the desired range, such as between 0 and 2π.
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Angle Measurement in Radians
Angles can be measured in radians, where 2π radians equal one full rotation (360 degrees). Understanding how to convert and manipulate angles in radians is essential for solving problems involving coterminal angles and angle normalization.
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Finding Positive Angles Less Than or Equal to 2π
To find a positive angle less than or equal to 2π that is coterminal with a given angle, subtract multiples of 2π from the angle until the result is within the interval [0, 2π]. This process ensures the angle is expressed in its principal value range.
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