# 1.4 Inverse functions  (Page 6/11)

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$f\left(x\right)=\sqrt{x-4}$

$f\left(x\right)={x}^{3}+1$

a. ${f}^{-1}\left(x\right)=\sqrt{x-1}$ b. Domain: all real numbers, range: all real numbers

$f\left(x\right)={\left(x-1\right)}^{2},x\le 1$

$f\left(x\right)=\sqrt{x-1}$

a. ${f}^{-1}\left(x\right)={x}^{2}+1,$ b. Domain: $x\ge 0,$ range: $y\ge 1$

$f\left(x\right)=\frac{1}{x+2}$

For the following exercises, use the graph of $f$ to sketch the graph of its inverse function.      For the following exercises, use composition to determine which pairs of functions are inverses.

$f\left(x\right)=8x,g\left(x\right)=\frac{x}{8}$

These are inverses.

$f\left(x\right)=8x+3,g\left(x\right)=\frac{x-3}{8}$

$f\left(x\right)=5x-7,g\left(x\right)=\frac{x+5}{7}$

These are not inverses.

$f\left(x\right)=\frac{2}{3}x+2,g\left(x\right)=\frac{3}{2}x+3$

$f\left(x\right)=\frac{1}{x-1},x\ne 1,g\left(x\right)=\frac{1}{x}+1,x\ne 0$

These are inverses.

$f\left(x\right)={x}^{3}+1,g\left(x\right)={\left(x-1\right)}^{1\text{/}3}$

$f\left(x\right)={x}^{2}+2x+1,x\ge -1,\phantom{\rule{1em}{0ex}}g\left(x\right)=-1+\sqrt{x},x\ge 0$

These are inverses.

$f\left(x\right)=\sqrt{4-{x}^{2}},0\le x\le 2,g\left(x\right)=\sqrt{4-{x}^{2}},0\le x\le 2$

For the following exercises, evaluate the functions. Give the exact value.

${\text{tan}}^{-1}\left(\frac{\sqrt{3}}{3}\right)$

$\frac{\pi }{6}$

${\text{cos}}^{-1}\left(-\frac{\sqrt{2}}{2}\right)$

${\text{cot}}^{-1}\left(1\right)$

$\frac{\pi }{4}$

${\text{sin}}^{-1}\left(-1\right)$

${\text{cos}}^{-1}\left(\frac{\sqrt{3}}{2}\right)$

$\frac{\pi }{6}$

$\text{cos}\left({\text{tan}}^{-1}\left(\sqrt{3}\right)\right)$

$\text{sin}\left({\text{cos}}^{-1}\left(\frac{\sqrt{2}}{2}\right)\right)$

$\frac{\sqrt{2}}{2}$

${\text{sin}}^{-1}\left(\text{sin}\left(\frac{\pi }{3}\right)\right)$

${\text{tan}}^{-1}\left(\text{tan}\left(-\frac{\pi }{6}\right)\right)$

$-\frac{\pi }{6}$

The function $C=T\left(F\right)=\left(5\text{/}9\right)\left(F-32\right)$ converts degrees Fahrenheit to degrees Celsius.

1. Find the inverse function $F={T}^{-1}\left(C\right)$
2. What is the inverse function used for?

[T] The velocity V (in centimeters per second) of blood in an artery at a distance x cm from the center of the artery can be modeled by the function $V=f\left(x\right)=500\left(0.04-{x}^{2}\right)$ for $0\le x\le 0.2.$

1. Find $x={f}^{-1}\left(V\right).$
2. Interpret what the inverse function is used for.
3. Find the distance from the center of an artery with a velocity of 15 cm/sec, 10 cm/sec, and 5 cm/sec.

a. $x={f}^{-1}\left(V\right)=\sqrt{0.04-\frac{V}{500}}$ b. The inverse function determines the distance from the center of the artery at which blood is flowing with velocity V . c. 0.1 cm; 0.14 cm; 0.17 cm

A function that converts dress sizes in the United States to those in Europe is given by $D\left(x\right)=2x+24.$

1. Find the European dress sizes that correspond to sizes 6, 8, 10, and 12 in the United States.
2. Find the function that converts European dress sizes to U.S. dress sizes.
3. Use part b. to find the dress sizes in the United States that correspond to 46, 52, 62, and 70.

[T] The cost to remove a toxin from a lake is modeled by the function

$C\left(p\right)=75p\text{/}\left(85-p\right),$ where $C$ is the cost (in thousands of dollars) and $p$ is the amount of toxin in a small lake (measured in parts per billion [ppb]). This model is valid only when the amount of toxin is less than 85 ppb.

1. Find the cost to remove 25 ppb, 40 ppb, and 50 ppb of the toxin from the lake.
2. Find the inverse function. c. Use part b. to determine how much of the toxin is removed for $50,000. a.$31,250, $66,667,$107,143 b. $\left(p=\frac{85C}{C+75}\right)$ c. 34 ppb

[T] A race car is accelerating at a velocity given by

$v\left(t\right)=\frac{25}{4}t+54,$

where v is the velocity (in feet per second) at time t .

1. Find the velocity of the car at 10 sec.
2. Find the inverse function.
3. Use part b. to determine how long it takes for the car to reach a speed of 150 ft/sec.

[T] An airplane’s Mach number M is the ratio of its speed to the speed of sound. When a plane is flying at a constant altitude, then its Mach angle is given by $\mu =2{\text{sin}}^{-1}\left(\frac{1}{M}\right).$

Find the Mach angle (to the nearest degree) for the following Mach numbers. 1. $\mu =1.4$
2. $\mu =2.8$
3. $\mu =4.3$

a. $~92\text{°}$ b. $~42\text{°}$ c. $~27\text{°}$

[T] Using $\mu =2{\text{sin}}^{-1}\left(\frac{1}{M}\right),$ find the Mach number M for the following angles.

1. $\mu =\frac{\pi }{6}$
2. $\mu =\frac{2\pi }{7}$
3. $\mu =\frac{3\pi }{8}$

[T] The temperature (in degrees Celsius) of a city in the northern United States can be modeled by the function

$T\left(x\right)=5+18\phantom{\rule{0.1em}{0ex}}\text{sin}\left[\frac{\pi }{6}\left(x-4.6\right)\right],$

where $x$ is time in months and $x=1.00$ corresponds to January 1. Determine the month and day when the temperature is $21\text{°}\text{C}.$

$x\approx 6.69,8.51;$ so, the temperature occurs on June 21 and August 15

[T] The depth (in feet) of water at a dock changes with the rise and fall of tides. It is modeled by the function

$D\left(t\right)=5\phantom{\rule{0.1em}{0ex}}\text{sin}\left(\frac{\pi }{6}t-\frac{7\pi }{6}\right)+8,$

where $t$ is the number of hours after midnight. Determine the first time after midnight when the depth is 11.75 ft.

[T] An object moving in simple harmonic motion is modeled by the function

$s\left(t\right)=-6\phantom{\rule{0.1em}{0ex}}\text{cos}\left(\frac{\pi t}{2}\right),$

where $s$ is measured in inches and $t$ is measured in seconds. Determine the first time when the distance moved is 4.5 ft.

$~1.5\phantom{\rule{0.2em}{0ex}}\text{sec}$

[T] A local art gallery has a portrait 3 ft in height that is hung 2.5 ft above the eye level of an average person. The viewing angle $\theta$ can be modeled by the function

$\theta ={\text{tan}}^{-1}\frac{5.5}{x}-{\text{tan}}^{-1}\frac{2.5}{x},$

where $x$ is the distance (in feet) from the portrait. Find the viewing angle when a person is 4 ft from the portrait.

[T] Use a calculator to evaluate ${\text{tan}}^{-1}\left(\text{tan}\left(2.1\right)\right)$ and ${\text{cos}}^{-1}\left(\text{cos}\left(2.1\right)\right).$ Explain the results of each.

${\text{tan}}^{-1}\left(\text{tan}\left(2.1\right)\right)\approx -1.0416;$ the expression does not equal 2.1 since $2.1>1.57=\frac{\pi }{2}$ —in other words, it is not in the restricted domain of $\text{tan}\phantom{\rule{0.1em}{0ex}}x.\phantom{\rule{0.2em}{0ex}}{\text{cos}}^{-1}\left(\text{cos}\left(2.1\right)\right)=2.1,$ since 2.1 is in the restricted domain of $\text{cos}\phantom{\rule{0.1em}{0ex}}x.$

[T] Use a calculator to evaluate $\text{sin}\left({\text{sin}}^{-1}\left(-2\right)\right)$ and $\text{tan}\left({\text{tan}}^{-1}\left(-2\right)\right).$ Explain the results of each.

#### Questions & Answers

find the domain and range of f(x)= 4x-7/x²-6x+8
Nick Reply
find the range of f(x)=(x+1)(x+4)
Jane Reply
-1, -4
Marcia
That's domain. The range is [-9/4,+infinity)
Jacob
If you're using calculus to find the range, you have to find the extrema through the first derivative test and then substitute the x-value for the extrema back into the original equation.
Jacob
Good morning,,, how are you
Harrieta Reply
d/dx{1/y - lny + X^3.Y^5}
mogomotsi Reply
How to identify domain and range
Umar Reply
hello
Akpevwe
He,,
Harrieta
hi
Dr
hello
velocity
I only talk to girls
Dr
women are smart then guys
Dr
Smarter
Adri
sorry
Dr
hi adri ana
Dr
:(
Shun
was up
Dr
hello
Adarsh
is it chatting app?.. I do not see any calculus here. lol
Adarsh
Find the arc length of the graph of f(x) = In (sinx) on the interval [Π/4, Π/2].
mukul Reply
Sand falling freely from a lorry form a conical shape whose height is always equal to one-third the radius of the base. a. How fast is the volume increasing when the radius of the base is (1m) and increasing at the rate of 1/4cm/sec Pls help me solve
ade
show that lim f(x) + lim g(x)=m+l
BARNABAS Reply
list the basic elementary differentials
Chio Reply
Differentiation and integration
Okikiola Reply
yes
Damien
proper definition of derivative
Syed Reply
the maximum rate of change of one variable with respect to another variable
Amdad
terms of an AP is 1/v and the vth term is 1/u show that the sum of uv terms is 1/2(uv+1)
Inembo Reply
what is calculus?
BISWAJIT Reply
calculus is math that studies the change in math, such as the rate and distance,
Tamarcus
what are the topics in calculus
Augustine
what is limit of a function?
Geoffrey Reply
what is x and how x=9.1 take?
Pravin Reply
what is f(x)
Inembo Reply
the function at x
Marc
also known as the y value so I could say y=2x or f(x)= 2x same thing just using functional notation your next question is what is dependent and independent variables. I am Dyslexic but know math and which is which confuses me. but one can vary the x value while y depends on which x you use. also
Marc
up domain and range
Marc
enjoy your work and good luck
Marc
I actually wanted to ask another questions on sets if u dont mind please?
Inembo
I have so many questions on set and I really love dis app I never believed u would reply
Inembo
Hmm go ahead and ask you got me curious too much conversation here
Adri
am sorry for disturbing I really want to know math that's why *I want to know the meaning of those symbols in sets* e.g n,U,A', etc pls I want to know it and how to solve its problems
Inembo
and how can i solve a question like dis *in a group of 40 students, 32 offer maths and 24 offer physics and 4 offer neither maths nor physics , how many offer both maths and physics*
Inembo
next questions what do dy mean by (A' n B^c)^c'
Inembo
The sets help you to define the function. The function is like a magic box where you put inside stuff(numbers or sets) and you get out the stuff but in different shapes (forms).
Adri
I dont understand what you wanna say by (A' n B^c)^c'
Adri
(A' n B (rise to the power of c)) all rise to the power of c
Inembo
Aaaahh
Adri
Ok so the set is formed by vectors and not numbers
Adri
A vector of length n
Adri
But you can make a set out of matrixes as well
Adri
I I don't even understand sets I wat to know d meaning of all d symbolsnon sets
Inembo
Wait what's your math level?
Adri
High-school?
Adri
yes
Inembo
am having big problem understanding sets more than other math topics
Inembo
So f:R->R means that the function takes real numbers and provides real numer. For ex. If f(x) =2x this means if you give to your function a real number like 2,it gives you also a real number 2times2=4
Adri
pls answer this question *in a group of 40 students, 32 offer maths and 24 offer physics and 4 offer neither maths nor physics , how many offer both maths and physics*
Inembo
If you have f:R^n->R^n you give to your function a vector of length n like (a1,a2,...an) where all a1,.. an are reals and gives you also a vector of length n... I don't know if i answering your question. Otherwise on YouTube you havr many videos where they explain it in a simple way
Adri
I would say 24
Adri
Offer both
Adri
Sorry 20
Adri
Actually you have 40 - 4 =36 who offer maths or physics or both.
Adri
I know its 20 but how to prove it
Inembo
You have 32+24=56who offer courses
Adri
56-36=20 who give both courses... I would say that
Adri
solution: In a question involving sets and Venn diagram, the sum of the members of set A + set B - the joint members of both set A and B + the members that are not in sets A or B = the total members of the set. In symbolic form n(A U B) = n(A) + n (B) - n (A and B) + n (A U B)'.
Mckenzie
In the case of sets A and B use the letters m and p to represent the sets and we have: n (M U P) = 40; n (M) = 24; n (P) = 32; n (M and P) = unknown; n (M U P)' = 4
Mckenzie
Now substitute the numerical values for the symbolic representation 40 = 24 + 32 - n(M and P) + 4 Now solve for the unknown using algebra: 40 = 24 + 32+ 4 - n(M and P) 40 = 60 - n(M and P) Add n(M and P), as well, subtract 40 from both sides of the equation to find the answer.
Mckenzie
40 - 40 + n(M and P) = 60 - 40 - n(M and P) + n(M and P) Solution: n(M and P) = 20
Mckenzie
thanks
Inembo
Simpler form: Add the sums of set M, set P and the complement of the union of sets M and P then subtract the number of students from the total.
Mckenzie
n(M and P) = (32 + 24 + 4) - 40 = 60 - 40 = 20
Mckenzie

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