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Thread: Trig ratio

  1. #1
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    Trig ratio

    Given that √5 tanA=-2 and CosB=8/17 in ∆ABC
    State why we may assume that angle C is acute and determine the value of Sin C
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  2. #2
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    Re: Trig ratio

    You are going to start by pointing out that all angles in a triangle are between 0 and 180.
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  3. #3
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    Re: Trig ratio

    Quote Originally Posted by Larryprec View Post
    Given that √5 tanA=-2 and CosB=8/17 in ∆ABC
    State why we may assume that angle C is acute and determine the value of Sin C
    How many obtuse angles a possible in any triangle? The so what?
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  4. #4
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    Re: Trig ratio

    Considering angles in radians for a moment:
    $\tan \theta <0$ implies $\theta$ is in the second or fourth quadrants. You can remember this by the mnemonic All Students Take Calc. Starting from the first quadrant and working counter clockwise, we have
    All => All (sine, cosine, and tangent are all positive in the 1st quadrant),
    Students => Sine (the sine function is positive while cosine and tangent both negative in the 2nd quadrant),
    Take => Tangent (the tangent function is positive while sine and cosine are both negative in the 3rd quadrant),
    Calc => Cosine (the cosine function is positive while sine and tangent are both negative in the 4th quadrant)
    Last edited by SlipEternal; May 4th 2018 at 07:33 AM.
    Thanks from Larryprec
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