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Math Help - trigonometry angles.

  1. #1
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    trigonometry angles.

    Hello fellow users, I have 2 questions, thanks in advance!

    Question 1:
    Angle z lies in the second quadrant and . Determine an exact value for sin2z.

    K, so when I attempted this question, I got 120/169, I am not sure if it is -120/169, or 120/169.


    Question 2:

    Given that , and y lies in the third quadrant, express as a difference between
    and an angle and then apply a confunction identity to find the measure of y.


    I legit have no idea what to do for this!
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  2. #2
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    Re: trigonometry angles.

    If angle z is in the second quadrant then \displaystyle \begin{align*} \cos{z} \end{align*} can not possibly have been \displaystyle \begin{align*} \frac{12}{13} \end{align*}...
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  3. #3
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    Re: trigonometry angles.

    Quote Originally Posted by Prove It View Post
    If angle z is in the second quadrant then \displaystyle \begin{align*} \cos{z} \end{align*} can not possibly have been \displaystyle \begin{align*} \frac{12}{13} \end{align*}...
    I meant -12/13
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  4. #4
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    Re: trigonometry angles.

    Well you know that in the second quadrant, \displaystyle \begin{align*} \sin{(z)} > 0 \end{align*} and \displaystyle \begin{align*} \cos{(z)} < 0 \end{align*}, so what do you think \displaystyle \begin{align*} \sin{(2z)} = 2\sin{(z)}\cos{(z)} \end{align*} has to be?
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  5. #5
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    Re: trigonometry angles.

    Quote Originally Posted by Prove It View Post
    Well you know that in the second quadrant, \displaystyle \begin{align*} \sin{(z)} > 0 \end{align*} and \displaystyle \begin{align*} \cos{(z)} < 0 \end{align*}, so what do you think \displaystyle \begin{align*} \sin{(2z)} = 2\sin{(z)}\cos{(z)} \end{align*} has to be?
    2(5/13)(-12/13)=-120/169? correct?
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  6. #6
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    Re: trigonometry angles.

    Yes, well done
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  7. #7
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    Re: trigonometry angles.

    Quote Originally Posted by Prove It View Post
    Yes, well done
    wow, you teach well, and you are very nice! thanks for the help!
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