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Homework Help: Trig Equations

  1. Apr 19, 2004 #1
    Solve 2cos^2(x)+cos(x)-1=0 In the interval where x is greater or equal to 0 and less than or equal to 2pi

    Let cos(x)=y

    2y^2+y-1=0 Factors to
    (2y-1)(y+1)=0
    so y=1/2 or y=-1
    cos(x)=-1 so x=pi
    cos(x)=1/2 Here is my question, I know it equals pi/3, but can it also equal 5pi/3 ?
    If someone would let me know I would greatly appreciate it
     
  2. jcsd
  3. Apr 19, 2004 #2
    Plug it into the equation. What do you get?

    cookiemonster
     
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