arcsin𝑥
25 asks the question "What positive number makes 25 when you square it?"
In other words, 𝑥2=25 has two solutions, but 𝑥 is only asking for the solution in 0,∞
arcsin12 asks the question "What angle in −𝜋2,𝜋2 makes 12 when you take the sine?"
In other words, sin𝜃=12 has an infinite number of solutions, but arcsin12 is only asking for the solution in −𝜋2,𝜋2 
Practice:
arcsin−1=