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    woodyp20's Avatar
    woodyp20 Posts: 12, Reputation: 1
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    #1

    Feb 16, 2011, 11:54 PM
    Sales of computer function problem
    The sales of a new model of notebook computer are approximated by: s(x)
    = 5000-13000e^-x/9 , where x represents the number of months the computer has been on the market and S represents sales in thousands of dollars. In how many months will the sales reach $2,600,000?
    ebaines's Avatar
    ebaines Posts: 12,130, Reputation: 1307
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    #2

    Feb 17, 2011, 07:16 AM

    I assume you mean this formula:



    You need to rearrange this to get x by itself. One concept to remember is that the inverse of the exponential function e^x is the natural logarithm, ln(x). Thus if A = e^b, then b = ln A. Other than that little trick the rest is straightforward algebra. Try it, and post back with what you get.
    woodyp20's Avatar
    woodyp20 Posts: 12, Reputation: 1
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    #3

    Feb 17, 2011, 10:34 PM
    Comment on ebaines's post
    I'm still confused with the inverse, could you set it up for me so I can see how its done?
    ebaines's Avatar
    ebaines Posts: 12,130, Reputation: 1307
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    #4

    Feb 18, 2011, 07:17 AM

    I'll give you an example of a similar problem - that way you can see how it's done and then apply the same technique to this problem.

    Suppse you have:



    Its inverse is found by getting the x variable all by itself:

    1. Subtract 10 from both side:



    2. Divide both sides by -3:



    3. Now take the natural log of both sides:



    4. Since , this means:



    5. Divide by -2:



    So now if you are given a value for y, you can determine the corresponding value of x. For example - suppose y = 4; then:



    Hope this helps - can you apply this same technique to your problem?

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