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Math Help - Trig Question

  1. #1
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    Trig Question

    Find the values of sinx and tanx if cosx=4/5 and x is in the first quadrant.
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  2. #2
    Super Member Quacky's Avatar
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    Re: Trig Question

    Draw yourself a right triangle with an unnamed angle \theta. We know the adjacent side is 4 units and the hypotenuse is 5 units.
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  3. #3
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    Re: Trig Question

    Okay, then I get sinx= 3/5 and tanx=3/4. Do I take the inverse of these to get my answer?
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  4. #4
    Super Member Quacky's Avatar
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    Re: Trig Question

    No, you're done. The question wanted you to find sin(x) and tan(x), indeed the inverses are ghastly numbers.
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  5. #5
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    Re: Trig Question

    Alternatively,

    Sin^2x+Cos^2x=1\Rightarrow\ Sin^2x=1-Cos^2x=1-\frac{16}{25}=\frac{25}{25}-\frac{16}{25}=\frac{9}{25}

    \Rightarrow\ Sinx=\frac{3}{5}

    as Sin(x) is positive in the first quadrant.

    Tanx=\frac{Sinx}{Cosx}=\frac{3\left(\frac{1}{5} \right)}{4\left(\frac{1}{5} \right)}=\frac{3}{4}
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