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Homework Help: Maths question

  1. Sep 2, 2010 #1
    1. The problem statement, all variables and given/known data

    Find X?
    1.732cos(x)-1.16=sin(x)

    Answer: X = 24.6
    2. Relevant equations



    3. The attempt at a solution

    sin(x) = sqrt(1-cos(x)^2)

    1.732cos(x)-1.16=sqrt(1-cos(x)^2)
    1.732^2 cos(x)^2 -1.16^2= 1-cos(x)^2
    3cos(x)^2-2.3456=1-cos(x)^2
    4cos(x)^2=3.3456
    cos(x)^2=3.34556/4
    x=23.8

    There when wrong?
     
  2. jcsd
  3. Sep 2, 2010 #2

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    You squared both sides in the first step, right?
    Well, the square of 1.732cos(x)-1.16 is not 1.732^2 cos(x)^2 -1.16^2.
    You can check it: (a - b)² is not a² - b² but (a - b)(a - b), then open up the brackets...
     
  4. Sep 2, 2010 #3
    ok thx.. mean i can use (a-b)^2=a^2-2ab+b^2?
     
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