# Math Help - Can anyone help me with this problem?

1. ## Can anyone help me with this problem?

If sin(x)=-4/5 and (x) is in Quadrant III, find tan(x/2)

2. ## Re: Can anyone help me with this problem?

Originally Posted by derek1008
If sin(x)=-4/5 and (x) is in Quadrant III, find tan(x/2)
if $x$ is a quad III angle ...

(1) by sketching a reference triangle in quad III, you can calculate the value of $\cos{x}$.

(2) $\pi < x < \frac{3\pi}{2} \implies \frac{\pi}{2} < \frac{x}{2} < \frac{3\pi}{4}$

... which says $\frac{x}{2}$ is a quad II angle. Therefore, $\tan\left(\frac{x}{2}\right) < 0$.

now use your half angle identity for tangent.