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Homework Help: Augmented matrices word problem - tiny issue

  1. Sep 21, 2014 #1
    1. The problem statement, all variables and given/known data
    Here is the problem from Stitz-Zeager Pre-calculus book:

    At 9 PM, the temperature was 60F; at midnight, the temperature was 50F; and at 6 AM,

    the temperature was 70F . Use the technique in Example 8.2.3 to t a quadratic function

    to these data with the temperature, T, measured in degrees Fahrenheit, as the dependent

    variable, and the number of hours after 9 PM, t, measured in hours, as the independent

    variable. What was the coldest temperature of the night? When did it occur?

    2. Relevant equations

    3. The attempt at a solution

    My question is about the number of hours as undependable variable:

    do you think authors mean x1=9, x2=3, x3=9 by saying "the number of hours after 9PM"? Or do you think it should be x1=9, x2=0, x3=6, or x1=9, x2=12, x3=6?
    I am confused :)

    Thank you!
  2. jcsd
  3. Sep 21, 2014 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    FWIW, 'undependable variable' = independent variable, in English. 'undependable' also means 'unreliable'.

    I'm afraid the wording of the problem is rather clear: the times are supposed to be taken as hours after 9 pm. You seem to want to impose your own time scale on the problem, using midnight as the origin of the time axis. So, for the reading taken at 9 pm, t = 0 hours, and the for reading taken at midnight, t = 3 hours. Eazy, peazy.
  4. Sep 21, 2014 #3
    Right! :) Thank you, SteamKing! And sorry for the typo - I can't find the way to edit that now; of course, it is "independent".
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