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Homework Help: Trigonomic Functions, Plotting from equation

  1. Mar 23, 2015 #1
    Hi All,

    Having a tough time with this one and i'm not sure why.
    Need to state amplitude, period and phase shift of f(x)=3cos2[x-(π/4)]+1.

    Amplitude being 3, period being 2π/2=π and phase shifted (π/4) to the right.
    Midline would also be at y=1

    Good so far?

    Right, so I know that 1/4 phase would be π/4 and therefore plotting five points from the initial (π/4,4) would give me (π/2, 1), (3π/4, -2), (π, 1), (5π/4, 4)

    But then plugging the initial equation into a graphing software it appears that the points do not line up.
    Can anyone confirm whether this is correct?
    I have been through ALL of Khan Academys videos and this lesson is driving me f'n nuts.

    ANY help appreciated. Cheers
  2. jcsd
  3. Mar 23, 2015 #2
    Everything you posted seems to be correct.

    Try typing this into the graphing software, the points should match up.

    [tex] f(x) = 3cos(2x-\pi/2)+1 [/tex]
  4. Mar 24, 2015 #3


    Staff: Mentor

    I agree with jbstemp that your work looks fine. Possibly how you typed the function into the graphing software is the problem. It probably wouldn't like 3cos2[x-(π/4)]+1, but should work with a few more parentheses, like this: 3cos(2 * (x-(π/4)))+1
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