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Math Help - Negative Exponantial Equation

  1. #1
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    Negative Exponantial Equation

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

    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:

    <br />
(X, Y)
    (1, -2)
    (2, 4)
    (3, -8)
    (-1, -\frac{1}{2})
    (-2, \frac{1}{4})
    (\frac{1}{2}, \sqrt {2}i)

    Could someone please explain to me how this works. Thanks.
    Attached Thumbnails Attached Thumbnails Negative Exponantial Equation-untitled-2.png  
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  2. #2
    Super Member Matt Westwood's Avatar
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    Quote Originally Posted by Korupt View Post
    I'm really confused by this. I have the equation:

    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:

    [HTML]<table cellpadding="1" cellspacing="1" border="1">
    <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]

    <br />
X | Y
    1 | -2
    2 | 4
    3 | -8
    -1 | -\frac{1}{2}
    -2 | \frac{1}{4}
    \frac{1}{2} | \sqrt {2}i

    Could someone please explain to me how this works. Thanks.
    It's probably done (-2)^x.
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  3. #3
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    Quote Originally Posted by Matt Westwood View Post
    It's probably done (-2)^x.
    What difference does that make?
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  4. #4
    Senior Member pacman's Avatar
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    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.
    Attached Thumbnails Attached Thumbnails Negative Exponantial Equation-y-2.gif   Negative Exponantial Equation-2-.gif  
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  5. #5
    Newbie gs.sh11's Avatar
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    -2^2 actually means (-1)2^2, which gives you -4 for the second ordered pair, so you probably made simple error's like that.
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  6. #6
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    Quote Originally Posted by pacman View Post
    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

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