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Typing exponents.

Spectral SwallowSpectral Swallow Registered User regular
edited August 2009 in Help / Advice Forum
So I've got this college class where we have to use a graphing calculator (my first time). So everything seems to be going smooth, when the problem ask me to graph an fractional exponent.
So I type in:
X^4/9
Which gets me the wrong angle.
Then I try X^(4/9) which gets me the right angle, but only half.

Graph.jpg

The top is what it SHOULD look like, the bottom is what it does. I've tried two different calculators with the same result. So is there something super duper obvious I'm missing or...?

I would ask the teacher, but it's an online class and she's made it quite clear she won't answer questions on the weekend.

Spectral Swallow on

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    Fuzzy Cumulonimbus CloudFuzzy Cumulonimbus Cloud Registered User regular
    edited August 2009
    No your graph is correct for the function you've given.
    Are you sure you have the function correct?

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    Spectral SwallowSpectral Swallow Registered User regular
    edited August 2009
    I think so, it says:
    graph2.jpg

    Which is the same as x^(4/9), right?

    Spectral Swallow on
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    Fuzzy Cumulonimbus CloudFuzzy Cumulonimbus Cloud Registered User regular
    edited August 2009
    when I graph x^4/9 I get the graph you got

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    Fuzzy Cumulonimbus CloudFuzzy Cumulonimbus Cloud Registered User regular
    edited August 2009
    in fact
    you can't even have points on the negative side
    anything raised to that exponent should be positive
    I've even tried .444444444
    same thing

    Fuzzy Cumulonimbus Cloud on
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    Spectral SwallowSpectral Swallow Registered User regular
    edited August 2009
    That's totally what I thought!
    I mean, here's a screencap of what it says though:

    graph3.jpg

    I've already completed the problem, it was just one of those things where it kinda bugged me that I couldn't get my graph to match the 'correct' one.

    Spectral Swallow on
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    PaleCommanderPaleCommander Registered User regular
    edited August 2009
    Well, here's my best guess:

    Your calculator appears to be trying to take X to the 1/9th power first, then raise it to the 4th power.

    For negative numbers, this might be causing it to choke on the imaginary intermediate results. This leads me to suggest two things.

    If you're using a TI-8something, the it might be handy to follow along in this manual on page 19:
    http://education.ti.com/downloads/guidebooks/graphing/83p/83m$book-eng.pdf

    Look in number display options, wherever they might be (probably the same place you set the number of decimal places to show; on a TI-83 it's accessed with MODE).

    If there's an option for how to display imaginary numbers on your calculator (if you see a setting marked "Real" or "a+bi"), make sure it's set to "a+bi" instead of real. This might let your calculator graph the left side of of your function without having a fit over the intermediate results. If this works, you shouldn't ever have similar problems again unless your settings get reset.

    The other option, if that doesn't work, is to force it to evaluate it in the correct order, e.g. use y1 = (x^4)^(1/9). This will make sure that it's never taking the root of a negative number.

    PaleCommander on
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    Spectral SwallowSpectral Swallow Registered User regular
    edited August 2009
    Awesome, that was what it was. What a weird problem.
    Thanks for both you guys' help.

    Spectral Swallow on
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