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Math Help - Advanced trig identity question! (involving addition formula)

  1. #1
    LHS
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    Exclamation Advanced trig identity question! (involving addition formula)



    Not quite sure how to do this, I messed about with it for a bit and got
    tan(theta)=0

    The answers in the book are 0,90

    Any help will be greatly appreciated!
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  2. #2
    Moo
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    Hello,
    Quote Originally Posted by LHS View Post


    Not quite sure how to do this, I messed about with it for a bit and got
    tan(theta)=0

    The answers in the book are 0,90

    Any help will be greatly appreciated!
    \sin \theta+\cos \theta=1

    Like they said, multiply by \frac{1}{\sqrt{2}}=\frac{\sqrt{2}}{2} :

    \frac{\sqrt{2}}{2} \sin \theta+\frac{\sqrt{2}}{2} \cos \theta=\frac{\sqrt{2}}{2}

    \cos 45 \sin \theta+\sin 45 \cos \theta=\frac{\sqrt{2}}{2}

    \sin(45+\theta)=\frac{\sqrt{2}}{2}
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  3. #3
    LHS
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    Ah, I see, I managed to get that equation but for some reason I didn't realise you could solve it, I expanded it then divided through by cos and sin to get tan theta + 1 = 1, which got me 0, and 180!

    Thanks!
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