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nezinau · Aug 11, 2009, 02:13 PM

Hello:) I must to solve: sin 2x=-1/2 :eek: could someone help me?? :D please, I need the answer as soon as possible:)
I saw that here was smth like that sin 2x=1/2 and if it is similar to mine, I'm very sorry:confused::confused:

galactus · Aug 11, 2009, 03:54 PM

$sin(2x)=\frac{-1}{2}$

$2x=sin^{-1}(\frac{-1}{2})$

$x=\frac{sin^{-1}(\frac{-1}{2})}{2}=\frac{-\pi}{12}$

But, this is only one solution. The period of sin(2x) is $\frac{2{\pi}}{2}={\pi}$

Add a multiple of ${\pi}$ to the solution.

$x=\frac{-\pi}{12}+C{\pi}$

There is another set of solutions as well.

$x=\frac{7{\pi}}{12}+C{\pi}$

Look at the graph and see why.

nezinau · Aug 12, 2009, 12:15 AM

Thank you very much for solution and quick replaying:) :D

galactus · Aug 12, 2009, 04:39 AM

I done that so you could see and have an example for future problems. The main point is, do you understand?

nezinau · Aug 12, 2009, 05:48 AM

Now I undestand because you explained me very well everything:)thank you again :D

nezinau · Aug 12, 2009, 12:44 PM

I would like to send you a personal message because I still have problems with this thing but I don't know how :(

Unknown008 · Aug 13, 2009, 10:21 AM

Just start other threads asking your questions :) We'll manage, don't worry. If we really have problems in understanding what you asked, then we'll see what to do, OK? :)

nezinau · Aug 14, 2009, 04:32 AM

Ok:D you know, I will be just in 11 grade so about this thing and it's solutions I understand anything and it 's needed not for me, but for my aunt. She do not undestand too:D she must to solve it step by step with all explanations so maybe you know where I could get information about mathematical tasks like this? :rolleyes: I would be very grateful for helping:rolleyes:
Sorry for the grammatical mistakes:o

galactus · Aug 14, 2009, 04:39 AM

Google, Google, Google. Also, get a hold of any nice algebra and trig book (The type used for a pre-calculus course), and practice the problems in the trig section. Solving trigonometric equations.

Google "Solving Trigonometric equations". There will be plenty of sites to visit.

One important thing to learn is how the periods of the various trig functions work.