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Richard
Lv 4
Richard asked in Science & MathematicsMathematics · 1 decade ago

cosA = -3/5 , A lies in quadrant 3. Find cosA/2?

Please explain w/steps

3 Answers

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  • henry_yang67
    Lv 6
    1 decade ago
    Favorite Answer

    you can use half angle directly

    cos A/2 = -sqrt((1+cosA)/2) = -sqrt(5)/5

    the angle A/2 is in Q II so it's negative

  • ?
    Lv 6
    1 decade ago

    (1+cosA)/2 =cos^2A/2 sq.root(1+cosA)/2=cosA/2 sq.root(1-3/5)=cosA/2 sq.root(2/5)=cosA/2

    A/2 is in 2nd quadrant so -sq.root(2/5)=cosA/2

  • Anonymous
    1 decade ago

    A=cos-1{-3.5}

    .: A= - cos-1{3.5}

    find it from natural cosine table.

    so u will get the value of A.

    now u can easily find cosA/2.

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