Why getting ValueError : Math domain error in trig. function, math.asin() ?

[jahuja73]

Unable to see why error in output.
Tried on repl.it, as well as ideone.com; and get the same error.

#your code goes here
import math
 
# number
a = 2
print("asin(",a,") is = ", math.asin(a))

Output:

Traceback (most recent call last):
File "./prog.py", line 6, in <module>
ValueError: math domain error