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Trigonometry - Inverse Functions and Equations

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Trigonometry - Inverse Functions and Equations - Page 1 preview imageStudy GuideTrigonometryInverse Functions and Equations1. Inverse Cosine and Inverse SineThe standard trigonometric functionslike sine and cosineareperiodic. This means they repeatthe same values over and over. Because of this repetition, the same output value can come frommany different input angles.This creates a problem:inverse functions can only exist if a function is one-to-one. To solve this,mathematicians restrict the domains of sine and cosine so that each output corresponds to exactlyone input.1.1Why Trigonometric Functions Need RestrictionsFigure 1 Sine function is not one to one.For a function to have an inverse, it must beone-to-one, which means:1.Each value in the domain maps to exactly one value in the range2.Each value in the range comes from exactly one value in the domainThe sine function fails this test because the same y-value occurs at many different x-values. This iswhy the sine function, as normally defined,does not have an inverse.To fix this, we restrict the domain so the function becomes one-to-one.
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Trigonometry - Inverse Functions and Equations - Page 2 preview imageStudy Guide1.2Restricting the Cosine FunctionFigure 2 Graph of restricted cosine function.To define the inverse cosine function, we restrict the domain of cosine to:This restricted function is written asCos x(note the capital “C”).Properties of the Restricted Cosine FunctionOn this interval, cosine decreases smoothly and never repeats values.1.3The Inverse Cosine FunctionTheinverse cosine functionis defined as the inverse of the restricted cosine function.
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Trigonometry - Inverse Functions and Equations - Page 3 preview imageStudy GuideFigure 3 Graph of inverse cosine function.It is written as:This means:(y) is the angle between (0) and (π)whose cosine is (x).Domain and Range of Inverse CosineImportant Cosine IdentitiesThese identities are only true when the domain restrictions are followed:
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Trigonometry - Inverse Functions and Equations - Page 4 preview imageStudy Guide1.4Restricting the Sine FunctionThe process for sine is very similar.Figure 4 Graph of restricted sine function.To make sine one-to-one, we restrict its domain to:This restricted function is written asSin x(capital “S”).Properties of the Restricted Sine FunctionOn this interval, sine increases smoothly without repeating values.
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Trigonometry - Inverse Functions and Equations - Page 5 preview imageStudy Guide1.5The Inverse Sine FunctionTheinverse sine functionis defined as the inverse of the restricted sine function.Figure 5 Graph of inverse sine function.It is written as:This means:(y) is the angle between-(π/2)and (π/2)whose sine is (x).Domain and Range of Inverse SineDomain:(-1 ≤ x ≤ 1)Range:-(π/2) ≤y ≤π/2Important Sine IdentitiesAgain, these identities depend on the restrictions:
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Trigonometry - Inverse Functions and Equations - Page 6 preview imageStudy Guide1.6Graphical Relationship Between Functions and Their InversesThe graphs of a function and its inverse are alwaysmirror imagesof each other across the line:Figure 6 Symmetry of inverse sine and cosine.This is true for:(y = cos x and y = cos-1x)(y = sin x and y = sin-1x)This symmetry helps explain why thedomain of one becomes the range of the other, and viceversa.Example 1:Evaluating an Inverse CosineProblemFind the exact value of:
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Trigonometry - Inverse Functions and Equations - Page 7 preview imageStudy GuideFigure 7 Drawing for Example 1.Step 1: Understand what inverse cosine meansIf:then this means:For inverse cosine, the anglemust be between (0) and (π).Step 2: Identify the reference angleWe know:Since the cosine value isnegative, the angle must be inQuadrant II(within the allowed range).
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Trigonometry - Inverse Functions and Equations - Page 8 preview imageStudy GuideStep 3: Find the correct angleFinal AnswerExample 2:Evaluating an Inverse SineProblemFind the exact value of:Figure 8 Drawing for Example 2.
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Trigonometry - Inverse Functions and Equations - Page 9 preview imageStudy GuideStep 1: Understand what inverse sine meansIf:then:For inverse sine, the anglemust be between-(π/2)and (π/2)Step 2: Identify the angleWe know:This angle lies within the allowed interval.Final AnswercExample 3:Using an Inverse IdentityProblemFind the exact value of:
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