# comparing graphs of functions

• Sep 22nd 2009, 12:11 PM
kyleu03
comparing graphs of functions
Compare the functions f(x) = x7 and g(x) = 7x by graphing both functions in several viewing rectangles. (a) Find all points of intersection of the graphs correct to one decimal place.
( 1, 2) (smaller x value)
( 3, 4) (larger x value)

I cant seem to find the points when i put it in my calculator. any help?
• Sep 22nd 2009, 01:44 PM
skeeter
Quote:

Originally Posted by kyleu03
Compare the functions f(x) = x7 and g(x) = 7x by graphing both functions in several viewing rectangles. (a) Find all points of intersection of the graphs correct to one decimal place.
( 1, 2) (smaller x value)
( 3, 4) (larger x value)

I cant seem to find the points when i put it in my calculator. any help?

what is the significance of the red 7 ?

is it an exponent in f(x) ?

is
$g(x) = 7x$ or $7^x$ ?

use a caret (^) symbol to denote exponents ... i.e. x^7 is x to the 7th power.
• Sep 22nd 2009, 04:49 PM
kyleu03
it is just the number, it is red because its changes. idk how to do it
• Sep 22nd 2009, 04:54 PM
mr fantastic
Quote:

Originally Posted by kyleu03
it is just the number, it is red because its changes. idk how to do it

This does not answer the questions raised and will just delay you getting a helpful reply. Re-post the equations. Use the conventional formatting for exponents (that is, powers).

Note: x^7 means $x^7$, 7^x means $7^x$,
• Sep 22nd 2009, 04:55 PM
skeeter
Quote:

Originally Posted by kyleu03
it is just the number, it is red because its changes. idk how to do it

x7 makes no sense. what is f(x) ?
• Sep 22nd 2009, 05:03 PM
kyleu03
ohh im very sorry i didnt see it posted wrong. it is

f(x) = x^7
g(x) = 7^x
• Sep 22nd 2009, 05:10 PM
skeeter
Quote:

Originally Posted by kyleu03
ohh im very sorry i didnt see it posted wrong. it is

f(x) = x^7
g(x) = 7^x

one solution should be obvious ...

graph $y = x^7 - 7^x$ and look for the the other zero ... easier to find.
• Sep 22nd 2009, 05:23 PM
kyleu03
"graph http://www.mathhelpforum.com/math-he...0760303a-1.gif and look for the the other zero " does not find the points of intersection for me
• Sep 22nd 2009, 07:37 PM
mr fantastic
Quote:

Originally Posted by kyleu03
"graph http://www.mathhelpforum.com/math-he...0760303a-1.gif and look for the the other zero " does not find the points of intersection for me

An obvious solution is a whole number that lies somewhere between 5 and 8 ....

The other solution solution cannot be found exactly. A decimal approximation lies somewhere between 1 and 2. You need to use your graph (or graphs) to estimate the value correct to 1 decimal place.

As to why you can't find the intersection points when you put it into your calculator, you should check:

1. that you've entered the correct equations.

2. you're using an appropriate window (check that ymin and ymax of the window are OK).
• Sep 22nd 2009, 08:12 PM
kyleu03
I was able to find the smaller, but not larger. any help?

Compare the functions f(x) = x7 and g(x) = 7x by graphing both functions in several viewing rectangles.
(a) Find all points of intersection of the graphs correct to one decimal place.
( 1http://www.webassign.net/wastatic/common/img/tick.png, 2http://www.webassign.net/wastatic/common/img/tick.png) (smaller x value)
( 3http://www.webassign.net/wastatic/common/img/cross.png, 4http://www.webassign.net/wastatic/common/img/cross.png) (larger x value)

(b) Which function grows more rapidly when x is large? 5
f(x)
g(x)

• Sep 22nd 2009, 08:15 PM
mr fantastic
Quote:

Originally Posted by mr fantastic
An obvious solution is a whole number that lies somewhere between 5 and 8 ....

The other solution solution cannot be found exactly. A decimal approximation lies somewhere between 1 and 2. You need to use your graph (or graphs) to estimate the value correct to 1 decimal place.

[snip]

Quote:

Originally Posted by kyleu03
I was able to find the smaller, but not larger. any help?
[snip]

There aren't many whole numbers between 5 and 7 that require testing ....
• Sep 22nd 2009, 08:47 PM
kyleu03
are you saying (0,7)
• Sep 22nd 2009, 08:50 PM
mr fantastic
Quote:

Originally Posted by kyleu03
are you saying (0,7)

I am saying that you should check what happens when x = 6 and x = 7.
• Sep 22nd 2009, 09:12 PM
kyleu03
thats wrong blong
• Sep 22nd 2009, 09:36 PM
mr fantastic
Quote:

Originally Posted by kyleu03
thats wrong blong

For crying out loud! $f(x) = x^7$ and $g(x) = 7^x$ have an intersection point at x = 7. The value of each function at x = 7 is 7^7. Given the previous replies, this should not have needed spelling out.