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Thread: trigonometry

  1. #1
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    trigonometry

    A and B are acute angles such that cosA=3/5 and cosB=5/12. find the value of cos(a+b). you are supposed to work it out without using your calculator.i am trying to work it out using the formula cos(A+B)=cosAcosB-sinAsinB however i dont know the value for A and B
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  2. #2
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    Re: trigonometry

    $\cos(a+b)=\cos(a)\cos(b) - \sin(a)\sin(b)$

    you are given $\cos(a)$ and $\cos(b)$

    what can you say about $\sin(a)$ and $\sin(b)$ ?

    hint: think of the most common trig identity
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