Math Is Fun Forum

camicat

Member

Registered: 2020-02-27

Posts: 11

Functions

Hello all,

I am having incredible difficulty understanding these problems. I understand the definition of domain and range, however I do not understand how I am supposed to find them from these given problems. On top of that, I have no idea how I am supposed to know how to draw the relation on a graph. Any help would be greatly appreciated!

C.  State the domain and range: Use the grid to draw the graph and verify your answer.  Be sure to label the scales on your axes to accommodate the numbers in the problem. (You may not use a computer program to draw the graphs for you.  The goal is to understand how to select points to draw a graph.)

5.  y = x^2 + 86

6.  y = 2x^3 + 8

7.  y = 40 - 8x^2

I see how they are in slope-intercept form, however I do not know how to graph them, because they all have exponents attached to x, and I don't know how that affects the graph.

Thanks in advance!

Bob

Administrator

Registered: 2010-06-20

Posts: 10,627

Re: Functions

hi camicat

It would probably help for a start if you had a look at this MIF page:

https://www.mathsisfun.com/algebra/quad … phing.html

It shows what a quadratic graph looks like (functions with x^2 in them) so that should help with 5 and 7.

6 is a cubic.  I cannot find a MIF page specifically on this but there is a function grapher here:

https://www.mathsisfun.com/data/function-grapher.php

The question says don't use a program to do the graphs for you, but there is no reason why you shouldn't use one to find out what similar graphs look like.  Once you've tried a few you'll get the hang of how the function relates to the shape of the graph, and then you should be able to work out what these graphs look like for yourself.

One other thing you can always do is to make a table of values.  The table needs two rows; one for your chosen x values; the second for the calculated y values using the equation for y in terms of x.  Then you can plot your points.  If you haven't got enough points yet to see what is going on, then choose some more x values and so get more points.

Slope/intercept form is usually only used for straight line graphs and these questions are all curves.  Hope that's enough to get you started.  If you want your answers to be checked post them back here.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob