Proving the Pythagorean Identity Practice Test

Using the Pythagorean identity $\sin^2(\theta)+\cos^2(\theta)=1$, if $\tan(\theta)=\frac{4}{3}$ and $\theta$ is in Quadrant III, what is $\cos(\theta)$?

Using the Pythagorean identity $\sin^2(\theta)+\cos^2(\theta)=1$, if $\sin(\theta)=\frac{3}{5}$ and $\theta$ is in Quadrant II, what is $\cos(\theta)$?​​