Built-in solutions
Python, 3*24=72 bytes
asin:
from math import*
s=asin
acos:
from math import*
c=acos
atan:
from math import*
t=atan
Python, 3*25=75 bytes (supports all real values)
asin:
from cmath import*
s=asin
acos:
from cmath import*
c=acos
atan:
from cmath import*
t=atan