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Math Help - Setting up an equation...

  1. #1
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    Setting up an equation...

    The desert temperature, H, oscillates daily between 36F at 6am and 76F at 6pm. Write a possible formula for H in terms of t, measured in hours from 6am. Use the form
    H = A cos(Bt) + C.

    Ok, so I'm setting this up like this...
    A = 20 (I subtracted 36 from 76 and divided it in half)
    B = 1pi/6 (the number of hours, 12 hours between 6am and 6pm and then reduced it)
    C = 36

    I know these values are wrong, but i cant set this up correctly can anyone help me out?
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  2. #2
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    Quote Originally Posted by JAMESveeder View Post
    The desert temperature, H, oscillates daily between 36F at 6am and 76F at 6pm. Write a possible formula for H in terms of t, measured in hours from 6am. Use the form
    H = A cos(Bt) + C.

    Ok, so I'm setting this up like this...
    A = 20 (I subtracted 36 from 76 and divided it in half)
    B = 1pi/6 (the number of hours, 12 hours between 6am and 6pm and then reduced it)
    C = 36

    I know these values are wrong, but i cant set this up correctly can anyone help me out?
    The value of A is ok as far as its size, but note that the curve starts at a low point, rises to a high point at mid-cycle, then returns to the low point. that would be a "flipped" cosine curve, wouldn't it?
    so ... what would you do to the value of A to show that?

    the period is 24 hours ... 6AM to 6PM is half a cycle.

    B = \frac{2\pi}{24} = \frac{\pi}{12}

    C = \frac{36+76}{2} = 56
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