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This figure shows three graphs labeled a, b, and c. Graph a shows an increasing function (f) along the x-axis and the y-axis which is labeled f of x. Graph b shows a decreasing function (f) along the x-axis and y-axis which is labeled f of x. Graph c shows a constant function (f) along the x-axis and y-axis which is labeled f of x. The constant function is horizontal. None of the graphs have any increments labeled on the x- or y-axis.

Increasing and decreasing functions

The slope determines if the function is an increasing linear function    , a decreasing linear function    , or a constant function.

  • f ( x ) = m x + b is an increasing function if m > 0.
  • f ( x ) = m x + b is a decreasing function if m < 0.
  • f ( x ) = m x + b is a constant function if m = 0.

Deciding whether a function is increasing, decreasing, or constant

Some recent studies suggest that a teenager sends an average of 60 texts per day http://www.cbsnews.com/8301-501465_162-57400228-501465/teens-are-sending-60-texts-a-day-study-says/ . For each of the following scenarios, find the linear function that describes the relationship between the input value and the output value. Then, determine whether the graph of the function is increasing, decreasing, or constant.

  1. The total number of texts a teen sends is considered a function of time in days. The input is the number of days, and output is the total number of texts sent.
  2. A teen has a limit of 500 texts per month in his or her data plan. The input is the number of days, and output is the total number of texts remaining for the month.
  3. A teen has an unlimited number of texts in his or her data plan for a cost of $50 per month. The input is the number of days, and output is the total cost of texting each month.

Analyze each function.

  1. The function can be represented as f ( x ) = 60 x where x is the number of days. The slope, 60, is positive so the function is increasing. This makes sense because the total number of texts increases with each day.
  2. The function can be represented as f ( x ) = 500 60 x where x is the number of days. In this case, the slope is negative so the function is decreasing. This makes sense because the number of texts remaining decreases each day and this function represents the number of texts remaining in the data plan after x days.
  3. The cost function can be represented as f ( x ) = 50 because the number of days does not affect the total cost. The slope is 0 so the function is constant.
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Interpreting slope as a rate of change

In the examples we have seen so far, the slope was provided to us. However, we often need to calculate the slope given input and output values. Recall that given two values for the input, x 1 and x 2 , and two corresponding values for the output, y 1 and y 2 —which can be represented by a set of points, ( x 1 y 1 ) and ( x 2 y 2 ) —we can calculate the slope m .

m = change in output (rise) change in input (run) = Δ y Δ x = y 2 y 1 x 2 x 1

Note that in function notation we can obtain two corresponding values for the output y 1 and y 2 for the function f , y 1 = f ( x 1 ) and y 2 = f ( x 2 ) , so we could equivalently write

m = f ( x 2 ) f ( x 1 ) x 2 x 1

[link] indicates how the slope of the line between the points, ( x 1 , y 1 ) and ( x 2 , y 2 ) , is calculated. Recall that the slope measures steepness, or slant. The greater the absolute value of the slope, the steeper the slant is.

This graph shows how to calculate the slope of a line. The line is graphed on an x y coordinate plane. The x-axis is labeled from negative 1 to 6. The y-axis is labeled from negative 1 to 10. The line passes through several points, but two are marked specifcally. The first is labeled (x subscript 1, y subscript 1). It is located at the point (1, 5). The second point is labeled (x subscript 2, y subscript 2). It is located at the point (2, 8). There is a small arrow that runs horizontally from point (2, 8) to point (1, 8). This arrow is labeled x subscript 2 minus x subscript 1. There is a blue arrow that runs vertically from point (1, 5) to point (1, 8) and is labeled y subscript 2 minus y subscript 1. Off to the side is the equation m equals delta y divided by delta x which equals y subscript 2 minus y subscript 1 divided by x subscript 2 minus x subscript 1.
The slope of a function is calculated by the change in y divided by the change in x . It does not matter which coordinate is used as the ( x 2 , y 2 ) and which is the ( x 1 , y 1 ) , as long as each calculation is started with the elements from the same coordinate pair.

Questions & Answers

Three charges q_{1}=+3\mu C, q_{2}=+6\mu C and q_{3}=+8\mu C are located at (2,0)m (0,0)m and (0,3) coordinates respectively. Find the magnitude and direction acted upon q_{2} by the two other charges.Draw the correct graphical illustration of the problem above showing the direction of all forces.
Kate Reply
To solve this problem, we need to first find the net force acting on charge q_{2}. The magnitude of the force exerted by q_{1} on q_{2} is given by F=\frac{kq_{1}q_{2}}{r^{2}} where k is the Coulomb constant, q_{1} and q_{2} are the charges of the particles, and r is the distance between them.
Muhammed
What is the direction and net electric force on q_{1}= 5µC located at (0,4)r due to charges q_{2}=7mu located at (0,0)m and q_{3}=3\mu C located at (4,0)m?
Kate Reply
what is the change in momentum of a body?
Eunice Reply
what is a capacitor?
Raymond Reply
Capacitor is a separation of opposite charges using an insulator of very small dimension between them. Capacitor is used for allowing an AC (alternating current) to pass while a DC (direct current) is blocked.
Gautam
A motor travelling at 72km/m on sighting a stop sign applying the breaks such that under constant deaccelerate in the meters of 50 metres what is the magnitude of the accelerate
Maria Reply
please solve
Sharon
8m/s²
Aishat
What is Thermodynamics
Muordit
velocity can be 72 km/h in question. 72 km/h=20 m/s, v^2=2.a.x , 20^2=2.a.50, a=4 m/s^2.
Mehmet
A boat travels due east at a speed of 40meter per seconds across a river flowing due south at 30meter per seconds. what is the resultant speed of the boat
Saheed Reply
50 m/s due south east
Someone
which has a higher temperature, 1cup of boiling water or 1teapot of boiling water which can transfer more heat 1cup of boiling water or 1 teapot of boiling water explain your . answer
Ramon Reply
I believe temperature being an intensive property does not change for any amount of boiling water whereas heat being an extensive property changes with amount/size of the system.
Someone
Scratch that
Someone
temperature for any amount of water to boil at ntp is 100⁰C (it is a state function and and intensive property) and it depends both will give same amount of heat because the surface available for heat transfer is greater in case of the kettle as well as the heat stored in it but if you talk.....
Someone
about the amount of heat stored in the system then in that case since the mass of water in the kettle is greater so more energy is required to raise the temperature b/c more molecules of water are present in the kettle
Someone
definitely of physics
Haryormhidey Reply
how many start and codon
Esrael Reply
what is field
Felix Reply
physics, biology and chemistry this is my Field
ALIYU
field is a region of space under the influence of some physical properties
Collete
what is ogarnic chemistry
WISDOM Reply
determine the slope giving that 3y+ 2x-14=0
WISDOM
Another formula for Acceleration
Belty Reply
a=v/t. a=f/m a
IHUMA
innocent
Adah
pratica A on solution of hydro chloric acid,B is a solution containing 0.5000 mole ofsodium chlorid per dm³,put A in the burret and titrate 20.00 or 25.00cm³ portion of B using melting orange as the indicator. record the deside of your burret tabulate the burret reading and calculate the average volume of acid used?
Nassze Reply
how do lnternal energy measures
Esrael
Two bodies attract each other electrically. Do they both have to be charged? Answer the same question if the bodies repel one another.
JALLAH Reply
No. According to Isac Newtons law. this two bodies maybe you and the wall beside you. Attracting depends on the mass och each body and distance between them.
Dlovan
Are you really asking if two bodies have to be charged to be influenced by Coulombs Law?
Robert
like charges repel while unlike charges atttact
Raymond
What is specific heat capacity
Destiny Reply
Specific heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree Celsius (or Kelvin). It is measured in Joules per kilogram per degree Celsius (J/kg°C).
AI-Robot
specific heat capacity is the amount of energy needed to raise the temperature of a substance by one degree Celsius or kelvin
ROKEEB
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Source:  OpenStax, Algebra and trigonometry. OpenStax CNX. Nov 14, 2016 Download for free at https://legacy.cnx.org/content/col11758/1.6
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