How do you use inverse trig functions to find angles?

1.$\arcsin \left(1\right) = \frac{\pi}{2}$
2. $\arctan \left(- 1\right) = - \frac{\pi}{4}$
3. $a r c \sec \left(\frac{1}{2}\right) = D N E$
4. $a r c \csc \left(- \sqrt{2}\right) = - \frac{\pi}{4}$