trigonometry

samy:

How do you know when to use inverse sin or sin?

sin(alpha)=opposite/hypotenuse

when you want to solve this equation to "alpha", then you need the inverse of sin, in this calculator "asin()".

asin( sin( alpha ) ) = asin( opposite/hypotenuse )
alpha = asin( opposite/hypotenuse )

so if "opposite" and a "hypotenuse" of a right triangle is given, you can calculate the angle "alpha".