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Section 7.5 Inverse Trigonometric Functions II Note: A calculator is helpful on some exercises. Bring one to class for this lecture. OBJECTIVE 1: Evaluating composite Functions involving Inverse Trigonometric Funcitons of −1 the Form f f and f −1 f It is imperative that you know and understand the three inverse trigonometric functions introduced in 7.4. € y = sin−1 x€ (Say: “y is the angle whose sine is x”) A. 1. Draw the graph of the inverse sine function. € 2. Domain___________________ Range _________________ 3. The range of the inverse sine function represents an angle whose terminal side lies in a. ____________________ (which quadrants) b. ___________________________________ (which axes) c. Show this with a graph. B. y = cos−1 x (Say: “y is the angle whose cosine is x”) 1. Draw the graph of the inverse cosine function. € 2. Domain___________________ Range _________________ 3. The range of the inverse cosine function represents an angle whose terminal side lies in a. ____________________ (which quadrants) b. ___________________________________ (which axes) c. Show this with a graph. C. y = tan−1 x (Say: “y is the angle whose tangent is x”) 1. Draw the graph of the inverse tangent function. € 2. Domain___________________ Range _________________ 3. The range of the inverse tangent function represents an angle whose terminal side lies in a. ____________________ (which quadrants) b. ___________________________________ (which axes) c. Show this with a graph. CAUTION: For trigonometric expressions of the form ( f f −1 )(x) or ( f −1 f )(x) , the cancellation equations work ONLY if x is in the domain of the “inner” function. € € Cancellation Equations for Compositions of Inverse Trigonometric Functions Cancellation Equations for the Restricted Sine Function and its Inverse for all x in the interval for all in the interval . Cancellation Equations for the Restricted Cosine Function and its Inverse for all x in the interval for all in the interval . Cancellation Equations for the Restricted Tangent Function and its Inverse for all x in the interval for all in the interval . . EXAMPLES: Find the exact value of each expression or state that it does not exist. 7.5.4 7.5.8 7.5.9 7.5.13 7.5.14 7.5.17 7.5.26 OBJECTIVE 2: Evaluating composite Functions involving Inverse Trigonometric Funcitons of −1 the Form f g and f −1 g Method: € 1. Evaluate € the “inner expression” and then evaluate the “outer expression.” 2. It may be necessary to draw a triangle (using x, y, or r) in the appropriate quadrant (depending on if the trig value is positive or negative), determine the value of the missing side and write the trig function requested in the “outer expression.” 3. If an exact value of the “inner expressions” cannot be determined, try writing the expressions as an equivalent expression using a cofunction identity. EXAMPLES. : Find the exact value of each expression or state that it does not exist. 7.5.32 7.5.34 7.5.37 7.5.40 7.5.43 7.5.46 OBJECTIVE 3: Functions Definition Understanding the Inverse cosecant, Inverse Secant, and Inverse Cotangent Inverse Cosecant Function The inverse cosecant function, denoted as of The domain of and the range is , is the inverse . is . Definition Inverse Secant Function The inverse secant function, denoted as , is the inverse of . The domain of is and the range is . Definition Inverse Cotangent Function The inverse cotangent function, denoted as , is the inverse of The domain of is . and the range is . EXAMPLES. : Find the exact value of each expression or state that it does not exist. 7.5.48 7.5.49 Most calculators do not have inverse cosecant, inverse secant, or inverse cotangent keys. To use a calculator, it is necessary to rewrite the given inverse cosecant, inverse secant, or inverse cotangent as an expression involving the inverse sine, inverse cosine, or inverse tangent respectively. EXAMPLES. Use a calculator to approximate each value or state that the value does not exist 7.5.51 7.5.52 OBJECTIVE 4: Writing Trigonometric Expressions as Algebraic Expressions Functions In Calculus, it is often necessary to write trigonometric expressions algebraically. In this text u is used as the unknown variable. In calculus x is often (but not always) used. We assume that the variable represents an angle whose terminal side is located in Quadrant I Method: € 1. Given the inverse trigonometric expression (inner expression which represents an unknown angle θ ), draw the triangle represented with θ in standard position and the terminal side located in QI 2. Label the given sides of the triangle. Since trigonometric expressions represent ratios of the sides of right triangles, two sides are always given. 3. Determine algebraically the 3€rd side. 4. Write the expression asked for (outside expression). EXAMPLES. Rewrite each trigonometric expression as an algebraic expression involving the variable u. Assume that u > 0 and that the value of the “inner” trigonometric expression represents an angle θ such π that 0 < θ < . 2 € € 7.5.54 € 7.5.55 7.5.57