Thread: Trig Half-Angle Formula question

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.

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

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