# 1 Trig/Precalc Chapter 4.7 Inverse trig functions Objectives Evaluate and graph the inverse sine function Evaluate and graph the remaining five inverse

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• *Trig/PrecalcChapter 4.7 Inverse trig functionsObjectivesEvaluate and graph the inverse sine functionEvaluate and graph the remaining five inverse trig functionsEvaluate and graph the composition of trig functions

• *The basic sine function fails the horizontal line test. It is not one-to-one so we cant find an inverse function unless we restrict the domain. Highlight the curve /2 < x < /2On the interval [-/2, /2] for sin x: the domain is [-/2, /2] and the range is [-1, 1]We switch x and y to get inverse functions So for f(x) = sin-1 x the domain is [-1, 1] and range is [-/2, /2] Therefore

• *Graphing the InverseWhen we get rid of all the duplicate numbers we get this curveNext we rotate it across the y=x line producing this curveFirst we draw the sin curve

• *Inverse sine function y = sin-1 x or y = arcsin xThe sine function gives us ratios representing opposite over hypotenuse in all 4 quadrants.

The inverse sine gives us the angle or arc length on the unit circle that has the given ratio. Remember the phrase arcsine of x is the angle or arc whose sine is x./2-/21

• *Evaluating Inverse Sine

If possible, find the exact value.arcsin(-1/2) = ____

We need to find the angle in the range [-/2, /2] such that sin y = -1/2

What angle has a sin of ? _______What quadrant would it be negative and within the range of arcsin? ____Therefore the angle would be ______

• *Evaluating Inverse Sine cont.b. sin-1( ) = ____ We need to find the angle in the range [-/2, /2] such that sin y =

What angle has a sin of ? _______What quadrant would it be positive and within the range of arcsin? ____Therefore the angle would be ______

c. sin-1(2) = _________ Sin domain is [-1, 1], therefore No solutionNo Solution

• *Graphs of Inverse Trigonometric FunctionsThe basic idea of the arc function is the same whether it is arcsin, arccos, or arctan

• *Inverse Functions Domains and Rangesy = arcsin xDomain: [-1, 1]Range:

y = arccos xDomain: [ -1, 1]Range:

y = arctan xDomain: (-, )Range:y = Arccos (x)

• *Evaluating Inverse Cosine

If possible, find the exact value.arccos((2)/2) = ____ We need to find the angle in the range [0, ] such that cos y = (2)/2

What angle has a cos of (2)/2 ? _______What quadrant would it be positive and within the range of arccos? ____Therefore the angle would be ______

b. cos-1(-1) = __ What angle has a cos of -1 ? _______

• *Warnings and Cautions!Inverse trig functions are equal to the arc trig function. Ex: sin-1 = arcsin

Inverse trig functions are NOT equal to the reciprocal of the trig function. Ex: sin-1 1/sin

There are NO calculator keys for: sec-1 x, csc-1 x, or cot-1 x

And csc-1 x 1/csc x sec-1 x 1/sec x cot-1 x 1/cot x

• *Evaluating Inverse functions with calculators ([E] 25 & 34)If possible, approximate to 2 decimal places.19. arccos(0.28) = ____

22. arctan(15) = _____

26. cos-1(0.26) = ____

• *Guided practice Example of [E] 28 & 30Use an inverse trig functionto write as a function of x. 28. Cos = 4/x so = cos-1(4/x) where x > 0

30. tan = (x 1)/(x2 1) = tan-1(x 1)/(x2 1) where x 1 > 0 , x > 1 as a function of x means to write an equation of the form equal to an expression with x in it.

• *Composition of trig functions

Find the exact value, sketch a triangle. cos(tan-1 (2)) = _____

This means tan = 2 sodraw the triangle Label the adjacent and opposite sides

Find the hypo. using Pyth. Theorem

So the215

• *ExampleWrite an algebraic expression that is equivalent to the given expression. cos(arctan(1/x))ux 11) Draw and label the triangle---(let u be the unknown angle) 2) Use the Pyth. Theo. to compute the hypo 3) Find the cot of u

• You Try! Evaluate: -4/3