Answer:
sin(x/2)
Explanation:
If we have a function such that f(x) = 2arcsinx, then the inverse will occur when the domain and ranges switch... in order words, we can switch y and x and then solve for y in order to get the inverse function.
let f(x) = y
y = 2 arcsinx
x = 2arcsinf(1(x))
sin(x/2) = f1(x)