# Section 4.6 Inverse Trigonometric fuctions

SECTION 4.6 INVERSE TRIGONOMETRIC FUCTIONS Objectives: -Evaluate and Graph inverse trig functions -Find compositions of trig functions Inverse SINE Is the sine function one-to-one?

No! Does not pass HLT. If we restrict the domain of the sine function to the interval [, ], the function IS one-to-one.

The inverse equation is y = sin -1x and is graphed by reflecting the restricted y = sinx in the line y = x. Inverse SINE Notice that the domain of the inverse is [1, 1] and its range is [, ]. Because angles and arcs given on the

unit circle have equivalent radian measures, the inverse sine function is sometimes referred to as the arcsine function y = arcsin x. Inverse SINE sin -1 x or y = arcsin x can be interpreted as the angle (or arc) between with a sine of x.

For example, sin-1 0.5 is the angle with a sine of 0.5. (30 degrees) Recall that sin t is the y-coordinate of the point on the unit circle that corresponds to the angle or arc length, t. Because the range of the inverse sine function are restricted,

the possible angle measures of the inverse sine function are located on the right half of the unit circle Example 1: Find the exact value, if it exists. A) B) arcsin C) D) Inverse COSINE

To make the cosine function one-to-one, the domain must be restricted to [0, ]. The inverse cosine function is y = cos -1x or arccosine function y = arccos x. The graph of y = cos -1 x is found by reflecting the graph of the restricted y = cosx in the line y = x.

Inverse COSINE Recall that cos t is the x-coordinate of the point on the unit circle that corresponds to the angle or arc length, t. Because the range of y = cos -1x is restricted to [0, ] , the possible angle measures of the

inverse cosine function are located on the upper half of the unit circle Example 2: Find the exact value, it exists. A) B) arccos C) D) Inverse TANGENT

To make the tangent function one-to-one, the domain must be restricted to (, ). The inverse tangent function is y = tan-1x or arctangent function y = arctan x. The graph of y = tan-1 x is found by reflecting the graph of the restricted y = tanx in the line y = x.

Unlike sine and cosine, the domain of the inverse tangent function is (-, ) Inverse TANGENT On the unit circle, tant = or tant =

The values of y = tan-1x will be located on the right half of the unit circle, not including and because the tangent function is undefined at those points. Example 3: Find the exact value, it exists. A) B) arctan 1

C) arctan () SUMMARY Graphing Inverse Trig Functions Rewrite the function in one of the following forms: sin y = x cos y = x tan y = x

Make a table of values, assigning radians from the restricted range to y. Plot the points and connect them with a smooth curve. Example 4: Sketch the

graph A) y = arctan y x Example 4: Sketch the graph B)

y= y x Example 4: Sketch the graph C) y= y

x Example 5: Application A) In a movie theater, a 32-foot-tall screen is located 8 feet above ground. Write a function modeling the viewing angle for a person in the theater whose eye-level when sitting is 6 feet above ground. Example 5: B) Determine the distance that corresponds

to the maximum viewing angle. Composition of Trig Functions In Lesson 1.7, you learned that if x is in the domain of f(x) and f -1(x) then f [f -1(x)] = x and f -1[f(x)] = x

Because the domains of the trig functions are restricted to obtain the inverse trig function, the properties do not apply for all values of x. For example, while sin x is defined for all x, the domain of sin-1 x is [-1,1]. Therefore, sin(sin-1 x) = x is only true when -1 x 1. A different restriction applies for the composition

of sin-1(sinx) because the domain of sin x is [, ]. Therefore, sin-1(sinx) = x is only true when SUMMARY of Composition Domain Restrictions Example 6: Find the exact value, if it exists A)

B) C) D) Example 7: Find the exact value A) B) C) Reciprocal Inverses

arccosecant (sec -1) arcsecant (csc -1) arccotangent (cot -1) EXTRA EXAMPLE: Find the exact value. A) B) C)

D) Example 8: A) Write cot (arccos x) as an algebraic expression of x that does not involve trigonometric functions. Example 8: B) Write cos(arctan x) as an algebraic expression of x that does not involve trigonometric functions.

Take A Picture For HW 1 7 sin tan 1. 24 2. csc cos

1 3 2

1 3 3. sin tan 4

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