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    Hi, I did a practise question for my tutor on trig Identities. The question was give the exact value for 2 sin 15 degrees cos 15 degrees.

    I couldn't find a rule to apply to this so I just took the question literally and put the figures in the calculator, showing each step.

    My tutor said that this was wrong and didn't give much explanation as to what I should do. I would be extremely grateful if someone could tell me how to go about this question.

    Thanks for reading.
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    (Original post by 153jam)
    Hi, I did a practise question for my tutor on trig Identities. The question was give the exact value for 2 sin 15 degrees cos 15 degrees.

    I couldn't find a rule to apply to this so I just took the question literally and put the figures in the calculator, showing each step.

    My tutor said that this was wrong and didn't give much explanation as to what I should do. I would be extremely grateful if someone could tell me how to go about this question.

    Thanks for reading.
    Note that sin(2x) = 2 sin x cos x.
    Thus 2 sin 15 cos 15 = sin(2*15) = sin(30) = 1/2.
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    You could apply a sine rule (I think its called the double angle formula): 2sinxcosx=sin2x

    so 2sin15cos15 = sin(2*15) which is sin30

    I think you are expected to know the exact value of sin30 so maybe that's what he was after?
 
 
 
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