The arcsine, [tex]\sin^{-1}[/tex], is the inverse of the [tex]\sin[/tex] function. This means that it takes as inputs what would usually be outputs for the [tex]\sin[/tex] function and produces as outputs what would usually be inputs for the [tex]\sin[/tex] function.
This can be particularly useful when you're trying to find an angle on a right triangle, but you've only been given the lengths of the sides. To find any angle [tex]\theta[/tex] in a right triangle, just take [tex]\sin^{-1} \frac{o}{h} [/tex], where o is the side opposite [tex]\theta[/tex] and h is the hypotenuse of the right triangle.
