In Exercises 55–62, use the properties of inverse functions f(f⁻¹ (x)) = x for all x in the domain of f⁻¹ and f⁻¹(f(x)) for all x in the domain of f, as well as the definitions of the inverse cotangent, cosecant, and secant functions, to find the exact value of each expression, if possible. sec(sec⁻¹ 7π)
Table of contents
- 0. Review of College Algebra4h 45m
- 1. Measuring Angles40m
- 2. Trigonometric Functions on Right Triangles2h 5m
- 3. Unit Circle1h 19m
- 4. Graphing Trigonometric Functions1h 19m
- 5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m
- 6. Trigonometric Identities and More Equations2h 34m
- 7. Non-Right Triangles1h 38m
- 8. Vectors2h 25m
- 9. Polar Equations2h 5m
- 10. Parametric Equations1h 6m
- 11. Graphing Complex Numbers1h 7m
5. Inverse Trigonometric Functions and Basic Trigonometric Equations
Inverse Sine, Cosine, & Tangent
Problem 69
Textbook Question
In Exercises 63–82, use a sketch to find the exact value of each expression. _ sin (cos⁻¹ √2/2)
Verified step by step guidance1
Recognize that the expression is \( \sin(\cos^{-1}(\frac{\sqrt{2}}{2})) \). Here, \( \cos^{-1} \) is the inverse cosine function, which gives an angle \( \theta \) such that \( \cos \theta = \frac{\sqrt{2}}{2} \).
Let \( \theta = \cos^{-1}(\frac{\sqrt{2}}{2}) \). This means \( \cos \theta = \frac{\sqrt{2}}{2} \). Our goal is to find \( \sin \theta \).
Recall the Pythagorean identity: \( \sin^2 \theta + \cos^2 \theta = 1 \). Substitute \( \cos \theta = \frac{\sqrt{2}}{2} \) into the identity to find \( \sin^2 \theta \):
\[ \sin^2 \theta = 1 - \cos^2 \theta = 1 - \left( \frac{\sqrt{2}}{2} \right)^2 \]
Simplify the expression inside the square root to find \( \sin^2 \theta \), then take the square root to find \( \sin \theta \):
\[ \sin \theta = \pm \sqrt{1 - \left( \frac{\sqrt{2}}{2} \right)^2} \]
Determine the correct sign of \( \sin \theta \) by considering the range of \( \cos^{-1} \), which is \( [0, \pi] \). Since \( \theta \) is in the first or second quadrant, \( \sin \theta \) is non-negative in the first quadrant and positive in the second quadrant. Use this to select the positive or negative root.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Inverse Cosine Function (cos⁻¹)
The inverse cosine function, cos⁻¹(x), returns the angle whose cosine is x, typically within the range 0 to π radians. It helps find an angle when the cosine value is known, which is essential for evaluating expressions like sin(cos⁻¹(x)).
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Right Triangle Interpretation of Trigonometric Functions
Trigonometric functions can be interpreted using right triangles, where cosine represents the adjacent side over hypotenuse. Using cos⁻¹(√2/2) gives an angle whose adjacent side and hypotenuse lengths can be used to find the opposite side, aiding in calculating sine of that angle.
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Introduction to Trigonometric Functions
Pythagorean Identity
The Pythagorean identity states that sin²θ + cos²θ = 1 for any angle θ. This identity allows us to find sin(θ) when cos(θ) is known by rearranging to sin(θ) = √(1 - cos²θ), which is crucial for evaluating sin(cos⁻¹(√2/2)).
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