Find a positive angle less than 2𝜋 that is coterminal with 16𝜋 3
Ch. 1 - Angles and the Trigonometric Functions

Chapter 1, Problem 5
In Exercises 1–8, use the Pythagorean Theorem to find the length of the missing side of each right triangle. Then find the value of each of the six trigonometric functions of θ.

Verified step by step guidance1
Identify the sides of the right triangle relative to angle \( \theta \) at vertex R. The hypotenuse is the side opposite the right angle, which is \( PR = 53 \). The side opposite \( \theta \) is \( PQ = 28 \), and the adjacent side to \( \theta \) is \( QR \), which is unknown.
Use the Pythagorean Theorem to find the missing side \( QR \). The theorem states:
\(QR^2 + PQ^2 = PR^2\)
Substitute the known values:
\(QR^2 + 28^2 = 53^2\)
Solve for \( QR^2 \):
\(QR^2 = 53^2 - 28^2\)
Then take the square root to find \( QR \):
\(QR = \sqrt{53^2 - 28^2}\)
Once you have the length of \( QR \), find the six trigonometric functions of \( \theta \) using the definitions relative to angle \( \theta \):
- \( \sin \theta = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{PQ}{PR} \)
- \( \cos \theta = \frac{\text{adjacent}}{\text{hypotenuse}} = \frac{QR}{PR} \)
- \( \tan \theta = \frac{\text{opposite}}{\text{adjacent}} = \frac{PQ}{QR} \)
- \( \csc \theta = \frac{1}{\sin \theta} = \frac{PR}{PQ} \)
- \( \sec \theta = \frac{1}{\cos \theta} = \frac{PR}{QR} \)
- \( \cot \theta = \frac{1}{\tan \theta} = \frac{QR}{PQ} \)
Substitute the known side lengths into these formulas to express each trigonometric function in terms of numbers. This completes the process of finding the missing side and the six trigonometric functions of \( \theta \).

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Pythagorean Theorem
The Pythagorean Theorem states that in a right triangle, the square of the hypotenuse (longest side) equals the sum of the squares of the other two sides. It is expressed as a² + b² = c², where c is the hypotenuse. This theorem helps find the missing side length when two sides are known.
Recommended video:
Solving Right Triangles with the Pythagorean Theorem
Right Triangle Trigonometric Functions
The six trigonometric functions—sine, cosine, tangent, cosecant, secant, and cotangent—relate the angles of a right triangle to the ratios of its sides. For an angle θ, sine is opposite/hypotenuse, cosine is adjacent/hypotenuse, and tangent is opposite/adjacent. The reciprocal functions are cosecant, secant, and cotangent.
Recommended video:
Introduction to Trigonometric Functions
Identifying Sides Relative to an Angle
In a right triangle, the side opposite the right angle is the hypotenuse. For a given angle θ, the side directly opposite is the opposite side, and the side next to θ (but not the hypotenuse) is the adjacent side. Correctly identifying these sides is essential for applying trigonometric functions accurately.
Recommended video:
Finding Missing Side Lengths
Related Practice
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Find the reference angle for 16𝜋 3
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The unit circle has been divided into twelve equal arcs, corresponding to t-values of
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Use the (x,y) coordinates in the figure to find the value of each trigonometric function at the indicated real number, t, or state that the expression is undefined.
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