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Homework Help: Find the Reference Angle for 11pi/4

  1. Sep 21, 2012 #1
    I understand perfectly how to find the reference angle for a degree, such as 150 degress = reference angle of 30 degrees, because the 2nd quadrant goes from 90 to 180 degrees, so you simply subtract 150 from 180 to come up with 30.

    I get that: 11pi/4 = 495 degrees. 495 degrees will give you a reference angle of 45 degress. Which I know how to convert to pi/4.
    HOWEVER, my solutions manual tells me that I should simply be subtracting 11pi/4 from 3pi. WHERE DOES THIS 3/PI COME FROM?!

    My trig class has not discussed the unit circle yet. It seems like I would have to understand that first?? Anyway, I kind of get how to solve the problem, but not in the way that I am supposed to. Please help!

  2. jcsd
  3. Sep 21, 2012 #2
    [itex]3\pi[/itex] is [itex]540^\circ[/itex]. [itex]540^\circ - 495^\circ = 45^\circ[/itex]. It's the same thing, just in radians.
  4. Sep 21, 2012 #3


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    3π radians, corresponds to 360° + 180° = 540°.

    540° - 495° = 45° , just as [itex]\displaystyle 3\pi-\frac{11\pi}{4}=\frac{\pi}{4}\ .[/itex]
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