# Graphing a funcion

• Feb 27th 2008, 02:34 AM
mt_lapin
Graphing a funcion
Graph the function.

$\displaystyle y=20\left(\frac{1}{4}\right)^{x}$

Is this table correct?

x/ f(x)
-3/ 1280
-2/ 320
-1/ 80
0/ 20
1/ 5
2/ (4/5)
3/ (5/16)

Also...how could I graph this by hand so that everyhting fits?

Thanks!
• Feb 27th 2008, 03:16 AM
Charbel

and to draw that you... get paper... and do dots :P and then do a lineee hehe =D

yer so ... make it the x values from say -3 to 3 and y from say... 1300 to ... 0?
• Feb 27th 2008, 03:22 AM
mt_lapin
Oh, you're right. It should be (5/4). Thanks for pointing it out (:
• Feb 27th 2008, 03:28 AM
Soroban
Hello, mt_lapin!

Quote:

Graph the function: .$\displaystyle y\:=\:20\left(\frac{1}{4}\right)^{x}$

Is this table correct?

. . $\displaystyle \begin{array}{c|c} x & f(x) \\ \hline -3&1280 \\ -2&320 \\ -1&80 \\ 0&20 \\ 1&5 \\ 2&\frac{4}{5} \\3 & \frac{5}{16} \end{array}$ . . . . . Yes!

Also...how could I graph this by hand so that everything fits?

Normally, no one expects a truly accurate graph.

Assuming that we know the shape of: .$\displaystyle [1]\;\;y \:=\:a^x$
. . we can sketch: .$\displaystyle [2]\;\;y \:=\:20\cdot4^{-x}$

It is basically a reflection of [1] over the y-axis.

Code:

          *      |                   |           *      |             *    |             *    |               *  |                   *20                   |    *                   |              *       - - - - - - + - - - - - - - - -                   |
• Feb 27th 2008, 03:47 AM
mt_lapin
Thank you so much Soroban! You've been a lot of help :)