<< Chapter < Page Chapter >> Page >

Evaluating functions

Given the function h ( p ) = p 2 + 2 p , evaluate h ( 4 ) .

To evaluate h ( 4 ) , we substitute the value 4 for the input variable p in the given function.

  h ( p ) = p 2 + 2 p   h ( 4 ) = ( 4 ) 2 + 2 ( 4 )          = 16 + 8          = 24

Therefore, for an input of 4, we have an output of 24.

Got questions? Get instant answers now!
Got questions? Get instant answers now!

Given the function g ( m ) = m 4 , evaluate g ( 5 ) .

g ( 5 ) = 1

Got questions? Get instant answers now!

Solving functions

Given the function h ( p ) = p 2 + 2 p , solve for h ( p ) = 3.

                  h ( p ) = 3             p 2 + 2 p = 3 Substitute the original function  h ( p ) = p 2 + 2 p .       p 2 + 2 p 3 = 0 Subtract 3 from each side .   ( p + 3 )( p 1 ) = 0 Factor .

If ( p + 3 ) ( p 1 ) = 0 , either ( p + 3 ) = 0 or ( p 1 ) = 0 (or both of them equal 0). We will set each factor equal to 0 and solve for p in each case.

( p + 3 ) = 0 , p = 3 ( p 1 ) = 0 , p = 1

This gives us two solutions. The output h ( p ) = 3 when the input is either p = 1 or p = 3. We can also verify by graphing as in [link] . The graph verifies that h ( 1 ) = h ( 3 ) = 3 and h ( 4 ) = 24.

Graph of a parabola with labeled points (-3, 3), (1, 3), and (4, 24).
Got questions? Get instant answers now!
Got questions? Get instant answers now!

Given the function g ( m ) = m 4 , solve g ( m ) = 2.

m = 8

Got questions? Get instant answers now!

Evaluating functions expressed in formulas

Some functions are defined by mathematical rules or procedures expressed in equation form. If it is possible to express the function output with a formula involving the input quantity, then we can define a function in algebraic form. For example, the equation 2 n + 6 p = 12 expresses a functional relationship between n and p . We can rewrite it to decide if p is a function of n .

Given a function in equation form, write its algebraic formula.

  1. Solve the equation to isolate the output variable on one side of the equal sign, with the other side as an expression that involves only the input variable.
  2. Use all the usual algebraic methods for solving equations, such as adding or subtracting the same quantity to or from both sides, or multiplying or dividing both sides of the equation by the same quantity.

Finding an equation of a function

Express the relationship 2 n + 6 p = 12 as a function p = f ( n ) , if possible.

To express the relationship in this form, we need to be able to write the relationship where p is a function of n , which means writing it as p = [ expression involving n ] .

2 n + 6 p = 12 6 p = 12 2 n Subtract  2 n  from both sides . p = 12 2 n 6 Divide both sides by 6 and simplify . p = 12 6 2 n 6 p = 2 1 3 n

Therefore, p as a function of n is written as

p = f ( n ) = 2 1 3 n
Got questions? Get instant answers now!
Got questions? Get instant answers now!

Expressing the equation of a circle as a function

Does the equation x 2 + y 2 = 1 represent a function with x as input and y as output? If so, express the relationship as a function y = f ( x ) .

First we subtract x 2 from both sides.

y 2 = 1 x 2

We now try to solve for y in this equation.

y = ± 1 x 2    = + 1 x 2  and  1 x 2

We get two outputs corresponding to the same input, so this relationship cannot be represented as a single function y = f ( x ) .

Got questions? Get instant answers now!
Got questions? Get instant answers now!

If x 8 y 3 = 0 , express y as a function of x .

y = f ( x ) = x 3 2

Got questions? Get instant answers now!

Are there relationships expressed by an equation that do represent a function but which still cannot be represented by an algebraic formula?

Yes, this can happen. For example, given the equation x = y + 2 y , if we want to express y as a function of x , there is no simple algebraic formula involving only x that equals y . However, each x does determine a unique value for y , and there are mathematical procedures by which y can be found to any desired accuracy. In this case, we say that the equation gives an implicit (implied) rule for y as a function of x , even though the formula cannot be written explicitly.

Questions & Answers

What are types of cell
Nansoh Reply
how can I get this book
Gatyin Reply
what is lump
Chineye Reply
what is cell
Maluak Reply
what is biology
Maluak
what's cornea?
Majak Reply
what are cell
Achol
Explain the following terms . (1) Abiotic factors in an ecosystem
Nomai Reply
Abiotic factors are non living components of ecosystem.These include physical and chemical elements like temperature,light,water,soil,air quality and oxygen etc
Qasim
what is biology
daniel Reply
what is diffusion
Emmanuel Reply
passive process of transport of low-molecular weight material according to its concentration gradient
AI-Robot
what is production?
Catherine
Pathogens and diseases
how did the oxygen help a human being
Achol Reply
how did the nutrition help the plants
Achol Reply
Biology is a branch of Natural science which deals/About living Organism.
Ahmedin Reply
what is phylogeny
Odigie Reply
evolutionary history and relationship of an organism or group of organisms
AI-Robot
ok
Deng
what is biology
Hajah Reply
cell is the smallest unit of the humanity biologically
Abraham
ok
Achol
what is biology
Victoria Reply
what is biology
Abraham
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Precalculus. OpenStax CNX. Jan 19, 2016 Download for free at https://legacy.cnx.org/content/col11667/1.6
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Precalculus' conversation and receive update notifications?

Ask