Trig Half-Angle Formula question

**mathmike2** · Oct 23rd 2010, 06:53 PM

Can anyone find my mistake in the above work. My book gives a different answer for the above question. The first line in the above is given by the book.

**Prove It** · Oct 23rd 2010, 10:07 PM

For starters, in the region $\displaystyle \pi < \theta < \frac{3\pi}{2}$ , you should know that $\sin{\theta} < 0,\cos{\theta} < 0$ and $\tan{\theta} > 0$ .

So check your starting values of $\sin{\theta}$ and $\cos{\theta}$ .

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