# Negative Exponantial Equation

• Oct 13th 2009, 12:28 PM
Korupt
Negative Exponantial Equation
I'm really confused by this. I have the equation:

$\displaystyle f(x) = -2^x$

According to Graph the function is supposed to look like the attached picture. But if you do an x-y table:

$\displaystyle (X, Y)$
$\displaystyle (1, -2)$
$\displaystyle (2, 4)$
$\displaystyle (3, -8)$
$\displaystyle (-1, -\frac{1}{2})$
$\displaystyle (-2, \frac{1}{4})$
$\displaystyle (\frac{1}{2}, \sqrt {2}i)$

Could someone please explain to me how this works. Thanks.
• Oct 13th 2009, 12:33 PM
Matt Westwood
Quote:

Originally Posted by Korupt
I'm really confused by this. I have the equation:

$\displaystyle f(x) = -2^x$

According to Graph the function is supposed to look like the attached picture. But if you do an x-y table:

<tr>
<td>x</td>
<td>y</td>
</tr>
<tr>
<td>1</td>
<td>-2</td>
</tr>
<tr>
<td>2</td>
<td>4</td>
</tr>
<tr>
<td>3</td>
<td>-8</td>
</tr>
</tr>
<tr>
<td>-1</td>
<td>-1/2</td>
</tr>
</tr>
<tr>
<td>-2</td>
<td>1/4</td>
</tr>
<tr>
<td>1/2</td>
<td>sqrt(2)i</td>
</tr>
<table>
[/HTML]

$\displaystyle X | Y$
$\displaystyle 1 | -2$
$\displaystyle 2 | 4$
$\displaystyle 3 | -8$
$\displaystyle -1 | -\frac{1}{2}$
$\displaystyle -2 | \frac{1}{4}$
$\displaystyle \frac{1}{2} | \sqrt {2}i$

Could someone please explain to me how this works. Thanks.

It's probably done $\displaystyle (-2)^x$.
• Oct 13th 2009, 12:36 PM
Korupt
Quote:

Originally Posted by Matt Westwood
It's probably done $\displaystyle (-2)^x$.

What difference does that make?
• Oct 13th 2009, 05:03 PM
pacman
Notice this two graphs

A) y = -(2^x)

and

B) y = (-2)^x

see the difference?

be careful with the sign "-". You may have plotted it like B instead of A.
• Oct 13th 2009, 05:11 PM
gs.sh11
$\displaystyle -2^2$ actually means $\displaystyle (-1)2^2$, which gives you -4 for the second ordered pair, so you probably made simple error's like that.
• Oct 13th 2009, 06:44 PM
Korupt
Quote:

Originally Posted by pacman
Notice this two graphs

A) y = -(2^x)

and

B) y = (-2)^x

see the difference?

be careful with the sign "-". You may have plotted it like B instead of A.

Thanks a bunch man, that clearer it up (Rofl)

@gs.sh11 No, $\displaystyle -2^2$ means $\displaystyle (-2)^2 = (-2)(-2) = 4$ Try putting the exponent in a calculator and see what you get. Your expression of $\displaystyle (-1)2^2$ would be $\displaystyle -(2^2)$