# 6.3 Inverse trigonometric functions  (Page 3/15)

 Page 3 / 15

Evaluate each of the following.

1. ${\text{sin}}^{-1}\left(-1\right)$
2. ${\mathrm{tan}}^{-1}\left(-1\right)$
3. ${\mathrm{cos}}^{-1}\left(-1\right)$
4. ${\mathrm{cos}}^{-1}\left(\frac{1}{2}\right)$

a. $\text{\hspace{0.17em}}-\frac{\pi }{2};\text{\hspace{0.17em}}$ b. $\text{\hspace{0.17em}}-\frac{\pi }{4};\text{\hspace{0.17em}}$ c. $\text{\hspace{0.17em}}\pi ;\text{\hspace{0.17em}}$ d. $\text{\hspace{0.17em}}\frac{\pi }{3}\text{\hspace{0.17em}}$

## Using a calculator to evaluate inverse trigonometric functions

To evaluate inverse trigonometric functions that do not involve the special angles discussed previously, we will need to use a calculator or other type of technology. Most scientific calculators and calculator-emulating applications have specific keys or buttons for the inverse sine, cosine, and tangent functions. These may be labeled, for example, SIN-1, ARCSIN, or ASIN.

In the previous chapter, we worked with trigonometry on a right triangle to solve for the sides of a triangle given one side and an additional angle. Using the inverse trigonometric functions, we can solve for the angles of a right triangle given two sides, and we can use a calculator to find the values to several decimal places.

In these examples and exercises, the answers will be interpreted as angles and we will use $\text{\hspace{0.17em}}\theta \text{\hspace{0.17em}}$ as the independent variable. The value displayed on the calculator may be in degrees or radians, so be sure to set the mode appropriate to the application.

## Evaluating the inverse sine on a calculator

Evaluate $\text{\hspace{0.17em}}{\mathrm{sin}}^{-1}\left(0.97\right)\text{\hspace{0.17em}}$ using a calculator.

Because the output of the inverse function is an angle, the calculator will give us a degree value if in degree mode and a radian value if in radian mode. Calculators also use the same domain restrictions on the angles as we are using.

In radian mode, $\text{\hspace{0.17em}}{\mathrm{sin}}^{-1}\left(0.97\right)\approx 1.3252.\text{\hspace{0.17em}}$ In degree mode, $\text{\hspace{0.17em}}{\mathrm{sin}}^{-1}\left(0.97\right)\approx 75.93°.\text{\hspace{0.17em}}$ Note that in calculus and beyond we will use radians in almost all cases.

Evaluate $\text{\hspace{0.17em}}{\mathrm{cos}}^{-1}\left(-0.4\right)\text{\hspace{0.17em}}$ using a calculator.

1.9823 or 113.578°

Given two sides of a right triangle like the one shown in [link] , find an angle.

1. If one given side is the hypotenuse of length $\text{\hspace{0.17em}}h\text{\hspace{0.17em}}$ and the side of length $\text{\hspace{0.17em}}a\text{\hspace{0.17em}}$ adjacent to the desired angle is given, use the equation $\text{\hspace{0.17em}}\text{\hspace{0.17em}}\theta ={\mathrm{cos}}^{-1}\left(\frac{a}{h}\right).$
2. If one given side is the hypotenuse of length $\text{\hspace{0.17em}}h\text{\hspace{0.17em}}$ and the side of length $\text{\hspace{0.17em}}p\text{\hspace{0.17em}}$ opposite to the desired angle is given, use the equation $\text{\hspace{0.17em}}\theta ={\mathrm{sin}}^{-1}\left(\frac{p}{h}\right).$
3. If the two legs (the sides adjacent to the right angle) are given, then use the equation $\text{\hspace{0.17em}}\theta ={\mathrm{tan}}^{-1}\left(\frac{p}{a}\right).$

## Applying the inverse cosine to a right triangle

Solve the triangle in [link] for the angle $\text{\hspace{0.17em}}\theta .$

Because we know the hypotenuse and the side adjacent to the angle, it makes sense for us to use the cosine function.

Solve the triangle in [link] for the angle $\text{\hspace{0.17em}}\theta .$

${\mathrm{sin}}^{-1}\left(0.6\right)=36.87°=0.6435\text{\hspace{0.17em}}$ radians

## Finding exact values of composite functions with inverse trigonometric functions

There are times when we need to compose a trigonometric function with an inverse trigonometric function. In these cases, we can usually find exact values for the resulting expressions without resorting to a calculator. Even when the input to the composite function is a variable or an expression, we can often find an expression for the output. To help sort out different cases, let $\text{\hspace{0.17em}}f\left(x\right)\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}g\left(x\right)\text{\hspace{0.17em}}$ be two different trigonometric functions belonging to the set $\text{\hspace{0.17em}}\left\{\mathrm{sin}\left(x\right),\mathrm{cos}\left(x\right),\mathrm{tan}\left(x\right)\right\}\text{\hspace{0.17em}}$ and let $\text{\hspace{0.17em}}{f}^{-1}\left(y\right)\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}{g}^{-1}\left(y\right)$ be their inverses.

How can you tell what type of parent function a graph is ?
generally by how the graph looks and understanding what the base parent functions look like and perform on a graph
William
if you have a graphed line, you can have an idea by how the directions of the line turns, i.e. negative, positive, zero
William
y=x will obviously be a straight line with a zero slope
William
y=x^2 will have a parabolic line opening to positive infinity on both sides of the y axis vice versa with y=-x^2 you'll have both ends of the parabolic line pointing downward heading to negative infinity on both sides of the y axis
William
y=x will be a straight line, but it will have a slope of one. Remember, if y=1 then x=1, so for every unit you rise you move over positively one unit. To get a straight line with a slope of 0, set y=1 or any integer.
Aaron
yes, correction on my end, I meant slope of 1 instead of slope of 0
William
what is f(x)=
I don't understand
Joe
Typically a function 'f' will take 'x' as input, and produce 'y' as output. As 'f(x)=y'. According to Google, "The range of a function is the complete set of all possible resulting values of the dependent variable (y, usually), after we have substituted the domain."
Thomas
Sorry, I don't know where the "Â"s came from. They shouldn't be there. Just ignore them. :-)
Thomas
Darius
Thanks.
Thomas
Â
Thomas
It is the Â that should not be there. It doesn't seem to show if encloses in quotation marks. "Â" or 'Â' ... Â
Thomas
Now it shows, go figure?
Thomas
what is this?
i do not understand anything
unknown
lol...it gets better
Darius
I've been struggling so much through all of this. my final is in four weeks 😭
Tiffany
this book is an excellent resource! have you guys ever looked at the online tutoring? there's one that is called "That Tutor Guy" and he goes over a lot of the concepts
Darius
thank you I have heard of him. I should check him out.
Tiffany
is there any question in particular?
Joe
I have always struggled with math. I get lost really easy, if you have any advice for that, it would help tremendously.
Tiffany
Sure, are you in high school or college?
Darius
Hi, apologies for the delayed response. I'm in college.
Tiffany
how to solve polynomial using a calculator
So a horizontal compression by factor of 1/2 is the same as a horizontal stretch by a factor of 2, right?
The center is at (3,4) a focus is at (3,-1), and the lenght of the major axis is 26
The center is at (3,4) a focus is at (3,-1) and the lenght of the major axis is 26 what will be the answer?
Rima
I done know
Joe
What kind of answer is that😑?
Rima
I had just woken up when i got this message
Joe
Rima
i have a question.
Abdul
how do you find the real and complex roots of a polynomial?
Abdul
@abdul with delta maybe which is b(square)-4ac=result then the 1st root -b-radical delta over 2a and the 2nd root -b+radical delta over 2a. I am not sure if this was your question but check it up
Nare
This is the actual question: Find all roots(real and complex) of the polynomial f(x)=6x^3 + x^2 - 4x + 1
Abdul
@Nare please let me know if you can solve it.
Abdul
I have a question
juweeriya
hello guys I'm new here? will you happy with me
mustapha
The average annual population increase of a pack of wolves is 25.
how do you find the period of a sine graph
Period =2π if there is a coefficient (b), just divide the coefficient by 2π to get the new period
Am
if not then how would I find it from a graph
Imani
by looking at the graph, find the distance between two consecutive maximum points (the highest points of the wave). so if the top of one wave is at point A (1,2) and the next top of the wave is at point B (6,2), then the period is 5, the difference of the x-coordinates.
Am
you could also do it with two consecutive minimum points or x-intercepts
Am
I will try that thank u
Imani
Case of Equilateral Hyperbola
ok
Zander
ok
Shella
f(x)=4x+2, find f(3)
Benetta
f(3)=4(3)+2 f(3)=14
lamoussa
14
Vedant
pre calc teacher: "Plug in Plug in...smell's good" f(x)=14
Devante
8x=40
Chris
Explain why log a x is not defined for a < 0
the sum of any two linear polynomial is what
Momo
how can are find the domain and range of a relations
the range is twice of the natural number which is the domain
Morolake
A cell phone company offers two plans for minutes. Plan A: $15 per month and$2 for every 300 texts. Plan B: $25 per month and$0.50 for every 100 texts. How many texts would you need to send per month for plan B to save you money?
6000
Robert
more than 6000
Robert
For Plan A to reach $27/month to surpass Plan B's$26.50 monthly payment, you'll need 3,000 texts which will cost an additional \$10.00. So, for the amount of texts you need to send would need to range between 1-100 texts for the 100th increment, times that by 3 for the additional amount of texts...
Gilbert
...for one text payment for 300 for Plan A. So, that means Plan A; in my opinion is for people with text messaging abilities that their fingers burn the monitor for the cell phone. While Plan B would be for loners that doesn't need their fingers to due the talking; but those texts mean more then...
Gilbert
can I see the picture