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Math Help - solve trigonometry equation

  1. #1
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    Exclamation solve trigonometry equation

    solve the equation

    2cos(squared)theta=1

    for 0(less than or equal to)theta(less than or equal to)2pie

    (4) marks
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  2. #2
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    Title: O dearrrrrrrrrrrrrrrrrrrrrrrrr!!!!!!!!!!!!!!
    Quote Originally Posted by eftheking View Post
    solve the equation

    2cos(squared)theta=1

    for 0(less than or equal to)theta(less than or equal to)2pie

    (4) marks
    \Rightarrow \cos \theta = \pm \frac{1}{\sqrt{2}}.

    There are now two simple equations to solve. Do so.

    And please refrain from the melodramatic titles.
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  3. #3
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    apologies.yes but that then gives me 0.9etc, and how do i plot that on the CAST diagrams.
    cos(-1)1/root2=0.9
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  4. #4
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    Quote Originally Posted by eftheking View Post
    apologies.yes but that then gives me 0.9etc, and how do i plot that on the CAST diagrams.
    cos(-1)1/root2=0.9
    This is wrong on three counts:

    1. It's a decimal approximation to an exact value. Go back and look over your notes relating to exact values of cos for special angles ......

    2. It's the wrong decimal approximation to the exact value.

    3. Cosine is also positive in the fourth quadrant, so you're only considering half of the solutions to \cos \theta = \frac{1}{\sqrt{2}}.
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  5. #5
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    wat is the key angle however
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  6. #6
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    Quote Originally Posted by eftheking View Post
    wat is the key angle however
    Did you do as suggested in my previous post and look over your notes relating to exact values of cos for special angles? (Don't answer - I already know the answer).

    \frac{\pi}{4}.
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