# What does sin(arc cos(2))+3cos(arctan(-1)) equal?

$\arccos$ is a function that is only defined on $\left[- 1 , 1\right]$ so $\arccos \left(2\right)$ doesn't exist.
On the other hand, $\arctan$ is defined on $\mathbb{R}$ so $\arctan \left(- 1\right)$ exists. It is an odd function so $\arctan \left(- 1\right) = - \arctan \left(1\right) = - \frac{\pi}{4}$.
So $3 \cos \left(\arctan \left(- 1\right)\right) = 3 \cos \left(- \frac{\pi}{4}\right) = 3 \cos \left(\frac{\pi}{4}\right) = \frac{3 \sqrt{2}}{2}$.