# 6.3 Inverse trigonometric functions  (Page 6/15)

 Page 6 / 15

Find a simplified expression for $\text{\hspace{0.17em}}\mathrm{sin}\left({\mathrm{tan}}^{-1}\left(4x\right)\right)\text{\hspace{0.17em}}$ for $\text{\hspace{0.17em}}-\frac{1}{4}\le x\le \frac{1}{4}.$

$\frac{4x}{\sqrt{16{x}^{2}+1}}$

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## Key concepts

• An inverse function is one that “undoes” another function. The domain of an inverse function is the range of the original function and the range of an inverse function is the domain of the original function.
• Because the trigonometric functions are not one-to-one on their natural domains, inverse trigonometric functions are defined for restricted domains.
• For any trigonometric function $\text{\hspace{0.17em}}f\left(x\right),\text{\hspace{0.17em}}$ if $\text{\hspace{0.17em}}x={f}^{-1}\left(y\right),\text{\hspace{0.17em}}$ then $\text{\hspace{0.17em}}f\left(x\right)=y.\text{\hspace{0.17em}}$ However, $\text{\hspace{0.17em}}f\left(x\right)=y\text{\hspace{0.17em}}$ only implies $\text{\hspace{0.17em}}x={f}^{-1}\left(y\right)\text{\hspace{0.17em}}$ if $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ is in the restricted domain of $\text{\hspace{0.17em}}f.\text{\hspace{0.17em}}$ See [link] .
• Special angles are the outputs of inverse trigonometric functions for special input values; for example, $\text{\hspace{0.17em}}\frac{\pi }{4}={\mathrm{tan}}^{-1}\left(1\right)\text{\hspace{0.17em}}\text{and}\text{\hspace{0.17em}}\frac{\pi }{6}={\mathrm{sin}}^{-1}\left(\frac{1}{2}\right).$ See [link] .
• A calculator will return an angle within the restricted domain of the original trigonometric function. See [link] .
• Inverse functions allow us to find an angle when given two sides of a right triangle. See [link] .
• In function composition, if the inside function is an inverse trigonometric function, then there are exact expressions; for example, $\text{\hspace{0.17em}}\mathrm{sin}\left({\mathrm{cos}}^{-1}\left(x\right)\right)=\sqrt{1-{x}^{2}}.\text{\hspace{0.17em}}$ See [link] .
• If the inside function is a trigonometric function, then the only possible combinations are $\text{\hspace{0.17em}}{\mathrm{sin}}^{-1}\left(\mathrm{cos}\text{\hspace{0.17em}}x\right)=\frac{\pi }{2}-x\text{\hspace{0.17em}}$ if $\text{\hspace{0.17em}}0\le x\le \pi \text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}{\mathrm{cos}}^{-1}\left(\mathrm{sin}\text{\hspace{0.17em}}x\right)=\frac{\pi }{2}-x\text{\hspace{0.17em}}$ if $\text{\hspace{0.17em}}-\frac{\pi }{2}\le x\le \frac{\pi }{2}.$ See [link] and [link] .
• When evaluating the composition of a trigonometric function with an inverse trigonometric function, draw a reference triangle to assist in determining the ratio of sides that represents the output of the trigonometric function. See [link] .
• When evaluating the composition of a trigonometric function with an inverse trigonometric function, you may use trig identities to assist in determining the ratio of sides. See [link] .

## Verbal

Why do the functions $\text{\hspace{0.17em}}f\left(x\right)={\mathrm{sin}}^{-1}x\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}g\left(x\right)={\mathrm{cos}}^{-1}x\text{\hspace{0.17em}}$ have different ranges?

The function $\text{\hspace{0.17em}}y=\mathrm{sin}x\text{\hspace{0.17em}}$ is one-to-one on $\text{\hspace{0.17em}}\left[-\frac{\pi }{2},\frac{\pi }{2}\right];\text{\hspace{0.17em}}$ thus, this interval is the range of the inverse function of $\text{\hspace{0.17em}}y=\mathrm{sin}x,$ $f\left(x\right)={\mathrm{sin}}^{-1}x.\text{\hspace{0.17em}}$ The function $\text{\hspace{0.17em}}y=\mathrm{cos}x\text{\hspace{0.17em}}$ is one-to-one on $\text{\hspace{0.17em}}\left[0,\pi \right];\text{\hspace{0.17em}}$ thus, this interval is the range of the inverse function of $\text{\hspace{0.17em}}y=\mathrm{cos}x,f\left(x\right)={\mathrm{cos}}^{-1}x.\text{\hspace{0.17em}}$

Since the functions $\text{\hspace{0.17em}}y=\mathrm{cos}\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}y={\mathrm{cos}}^{-1}x\text{\hspace{0.17em}}$ are inverse functions, why is $\text{\hspace{0.17em}}{\mathrm{cos}}^{-1}\left(\mathrm{cos}\left(-\frac{\pi }{6}\right)\right)\text{\hspace{0.17em}}$ not equal to $\text{\hspace{0.17em}}-\frac{\pi }{6}?$

Explain the meaning of $\text{\hspace{0.17em}}\frac{\pi }{6}=\mathrm{arcsin}\left(0.5\right).$

$\frac{\pi }{6}\text{\hspace{0.17em}}$ is the radian measure of an angle between $\text{\hspace{0.17em}}-\frac{\pi }{2}\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}\frac{\pi }{2}$ whose sine is 0.5.

Most calculators do not have a key to evaluate $\text{\hspace{0.17em}}{\mathrm{sec}}^{-1}\left(2\right).\text{\hspace{0.17em}}$ Explain how this can be done using the cosine function or the inverse cosine function.

Why must the domain of the sine function, $\text{\hspace{0.17em}}\mathrm{sin}\text{\hspace{0.17em}}x,\text{\hspace{0.17em}}$ be restricted to $\text{\hspace{0.17em}}\left[-\frac{\pi }{2},\frac{\pi }{2}\right]\text{\hspace{0.17em}}$ for the inverse sine function to exist?

In order for any function to have an inverse, the function must be one-to-one and must pass the horizontal line test. The regular sine function is not one-to-one unless its domain is restricted in some way. Mathematicians have agreed to restrict the sine function to the interval $\text{\hspace{0.17em}}\left[-\frac{\pi }{2},\frac{\pi }{2}\right]\text{\hspace{0.17em}}$ so that it is one-to-one and possesses an inverse.

#### Questions & Answers

what is set?
a colony of bacteria is growing exponentially doubling in size every 100 minutes. how much minutes will it take for the colony of bacteria to triple in size
I got 300 minutes. is it right?
Patience
no. should be about 150 minutes.
Jason
It should be 158.5 minutes.
Mr
ok, thanks
Patience
100•3=300 300=50•2^x 6=2^x x=log_2(6) =2.5849625 so, 300=50•2^2.5849625 and, so, the # of bacteria will double every (100•2.5849625) = 258.49625 minutes
Thomas
what is the importance knowing the graph of circular functions?
can get some help basic precalculus
What do you need help with?
Andrew
how to convert general to standard form with not perfect trinomial
can get some help inverse function
ismail
Rectangle coordinate
how to find for x
it depends on the equation
Robert
yeah, it does. why do we attempt to gain all of them one side or the other?
Melissa
whats a domain
The domain of a function is the set of all input on which the function is defined. For example all real numbers are the Domain of any Polynomial function.
Spiro
Spiro; thanks for putting it out there like that, 😁
Melissa
foci (–7,–17) and (–7,17), the absolute value of the differenceof the distances of any point from the foci is 24.
difference between calculus and pre calculus?
give me an example of a problem so that I can practice answering
x³+y³+z³=42
Robert
dont forget the cube in each variable ;)
Robert
of she solves that, well ... then she has a lot of computational force under her command ....
Walter
what is a function?
I want to learn about the law of exponent
explain this
what is functions?
A mathematical relation such that every input has only one out.
Spiro
yes..it is a relationo of orders pairs of sets one or more input that leads to a exactly one output.
Mubita
Is a rule that assigns to each element X in a set A exactly one element, called F(x), in a set B.
RichieRich