Determine the inner and outer functions. For example, in the composite function ArcCos (sin (45)), the inner function, commonly referred to as g(x), is sin (45). The outer function in this pair is Cos (g(x)).
Evaluate the inner function. The sin (45) = √(2) / 2.
Take the returned value from the inner function and pass it to the outer function. Specifically, ArcCos (sin (45)) = ArcCos ( √(2) / 2 ).
Evaluate the outer function. In conclusion, ArcCos ( √(2) / 2 ) = 45 degrees.