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Trig question

The question is solve the equation 2SinxCos2x + Sin2x = 0, i cant simplify it to a form where i can solve any ideas?
Reply 1
Express sin2x in terms of sinx and cosx then factorise the expression. Then use the fact that cosA+cosB=2cos12(A+B)cos12(AB) \cos A + \cos B = 2\cos \frac{1}{2} (A+B) \cos \frac{1}{2} (A-B) .
Reply 2
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.
Reply 3
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 cosA+cosB=2cos12(A+B)cos12(AB) \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
Reply 4
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?
Reply 5
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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