solve the equation cos 2theta = sin theta

Question

anonymous · Answer

I guess u can use the double angle formula ->

2sin = 2 sin cos ->

2sin cos -sin = 0 -> sin (2 cos -1) ->

sin = 0 or cos = 1/2.

chaise · Answer

anonymous · Answer

ummm estudier, where did 2 sin come from?

anonymous · Answer

Sorry, should be sin 2, rest is OK though. Trying to figure out why Wolfram doesn't get the 0.. http://www.wolframalpha.com/input/?i=cos+%282theta%29+-+sin%28theta%29+%3D+0

anonymous · Answer

huh? but  the question asks for sin theta, where did 2 sin come from?

anonymous · Answer

Oh, I see, I have done sin 2 theta instead of cos 2 theta...duh!

Let me do it again, sorry..

anonymous · Answer

OK, if I do Cos2 = 1- 2sin^2 = sin, I get a quadratic, let's see what that is....

anonymous · Answer

apology is accepted! =D LOLS @estudier, thats ok take your time darling!

anonymous · Answer

Right, so that's -1/2 plus minus root2 , I hope!!

anonymous · Answer

Still a bit odd, though....

anonymous · Answer

I must be sleeping, that-s not right, either..mom.

anonymous · Answer

Quadratic gives -1 plus minus 3 /4 

is plus  0.5 or -1

Phew!

anonymous · Answer

Now why Wolfram is different...

anonymous · Answer

It's picking up the 1/2 (and multiples) but doing something strange in the second quadrant.

anonymous · Answer

Let me have a think about it...

anonymous · Answer

oh well thanx anyways, dw about it i shall ask my math teacher tomorrow!

anonymous · Answer

Of course it is calculating theta, pi/6. 5pi/6, 3pi/2...

anonymous · Answer

u see? sin pi/6 = 1/2.

anonymous · Answer

ohhhhhh okkkk

anonymous · Answer

I'm awake now:-) Sorry to take your time...