Hey, I'm just like... completely zoned out:

sin x = cos ( 2x + 15 )

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- May 26th 2008, 06:24 PMKuczajsolve trigonometry equation
Hey, I'm just like... completely zoned out:

sin x = cos ( 2x + 15 ) - May 27th 2008, 04:34 AMtopsquark
- May 27th 2008, 05:28 PMKuczaj
Wow, thanks for that that, even you didn't solve for X. Anyways, I found the answer and it's 25.

- May 27th 2008, 06:08 PMReckoner
This is incorrect. For example, let $\displaystyle x = \frac{\pi}2$. The actual identity should be $\displaystyle \sin x = \cos\left(\frac{\pi}2 - x\right)$. Then we have:

$\displaystyle \cos\left(\frac{\pi}2 - x\right) = \cos(2x + 15)$

Note, however, that there will be infinitely many solutions due to the periodicity of the cosine.

And Kuczaj, did you even try your answer? I get

$\displaystyle \begin{array}{rcr@{.}l}

\sin 25^\circ & \approx & 0&42261826174\\

\cos\left(2\left(25^\circ\right) + 15\right) & \approx & -0&986467363994

\end{array}$