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    The question is solve the equation 2SinxCos2x + Sin2x = 0, i cant simplify it to a form where i can solve any ideas?
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    Express sin2x in terms of sinx and cosx then factorise the expression. Then use the fact that  \cos A + \cos B = 2\cos \frac{1}{2} (A+B) \cos \frac{1}{2} (A-B) .
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    (Original post by SunDun111)
    The question is solve the equation 2SinxCos2x + Sin2x = 0, i cant simplify it to a form where i can solve any ideas?
    As an alternative to using the sum to product identity shown above, you could also use an identity for cos(2x) and then solve the quadratic in cos.
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    (Original post by notnek)
    As an alternative to using the sum to product identity shown above, you could also use an identity for cos(2x) and then solve the quadratic in cos.
    (Original post by B_9710)
    Express sin2x in terms of sinx and cosx then factorise the expression. Then use the fact that  \cos A + \cos B = 2\cos \frac{1}{2} (A+B) \cos \frac{1}{2} (A-B) .
    Yeah i did it by forming a quadratic using 2SinX ( Cos2x + Cosx) = 0 hence forming a quadratic
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    (Original post by SunDun111)
    Yeah i did it by forming a quadratic using 2SinX ( Cos2x + Cosx) = 0 hence forming a quadratic
    We may or may not be talking about the same thing.

    I meant forming a quadratic to solve Cos2x + Cosx = 0.

    So are you okay now or still stuck?
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    (Original post by notnek)
    We may or may not be talking about the same thing.

    I meant forming a quadratic to solve Cos2x + Cosx = 0.

    So are you okay now or still stuck?
    Same thing i got it right according to the answer book

    the Q was 2SinxCos2x + Sin2x

    Rewriting Sin2x as 2SinxCosx

    Then factorising 2sinxCos2x + 2 SinxCosx as 2sinx (Cos 2x + cos x) then using an identity for cos2x to find a trig equation to solve.
 
 
 
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