don't know how to use double or half angle formula to solve the equation:

sin2x+cosx=0

in the interval [0, 2pi) and the answers are pi/2, 7pi/6, 3pi/2, 11pi/6

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- Feb 7th 2009, 02:15 PMguardofthecolor4everdouble or half angle formula to solve
don't know how to use double or half angle formula to solve the equation:

sin2x+cosx=0

in the interval [0, 2pi) and the answers are pi/2, 7pi/6, 3pi/2, 11pi/6 - Feb 7th 2009, 02:21 PMmr fantastic
Substitute $\displaystyle \sin (2x) = 2 \sin x \cos x$.

Now factorise the resulting expression. Now apply the null factor law to get two simple trig equations that you need to solve over the given interval:

$\displaystyle \cos x = 0$

$\displaystyle 2 \sin (x) + 1 = 0$ - Feb 7th 2009, 02:32 PMguardofthecolor4ever
thanks!