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    Question

    Find the exact value of

    cos120°
    A .5 Correct Answer Incorrect Answer
    B .05 Correct Answer Incorrect Answer
    C -.5 Correct Answer Incorrect Answer
    D -.05 Correct Answer Incorrect Answer

    Solution

    cos120° = cos (180°-60°) from cos(A-B) = cosA. cosB- sinA.sinB so cos180°.cos60°-sin 180°.sin60° =-1.1/2 -0. √3/2 =-1/2= -.5

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