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Thread: How do I solve cos(X-20degrees)= 1/2 ?

  1. #1
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    How do I solve cos(X-20degrees)= 1/2 ?

    This is the question. Please help!
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    Re: How do I solve cos(X-20degrees)= 1/2 ?

    Quote Originally Posted by Seirinaba View Post
    This is the question. Please help!
    $\cos\left(x-\frac{\pi}{9}\right)=\frac{1}{2}$ which implies that $\left(x-\frac{\pi}{9}\right)=\frac{\pi}{6}$.
    Therefore $x=\frac{\pi}{6}+\frac{\pi}{9}=\frac{5\pi}{18}$
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    Re: How do I solve cos(X-20degrees)= 1/2 ?

    how did you turn 1/2 into π/6?
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    Re: How do I solve cos(X-20degrees)= 1/2 ?

    Quote Originally Posted by Seirinaba View Post
    how did you turn 1/2 into π/6?
    As a matter of fact $\frac{1}{2}$ does not turn into $\frac{\pi}{6}$

    Because I do not know what a degree is, I chose to do mathematics using numbers.
    I just know and you must learn that if $\cos(\theta)=\frac{1}{2}$ then $\theta=\pm\frac{\pi}{6}$.
    That is just a fact of the measure of angles.
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    Re: How do I solve cos(X-20degrees)= 1/2 ?

    Quote Originally Posted by Seirinaba View Post
    This is the question. Please help!
    (5pi/18)radians = [(5pi/18)*1] radians = [(5pi/18)*(180degrees/pi radians)]radians = 50 degrees. I used the fact that 180 degrees/pi radians = 1
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    Re: How do I solve cos(X-20degrees)= 1/2 ?

    $\cos \frac{\pi }{3}=\frac{1}{2}$

    $x=\frac{\pi }{3}+\frac{\pi }{9}=\frac{4 \pi }{9}$

    80 degrees
    Last edited by Idea; Mar 18th 2018 at 03:15 AM.
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