Inverse trig undoes the ratio: arcsin(x) asks 'which principal angle has sine x?'. Recall the special-angle table in reverse.

Steps

1. Match the value to the special-angle table.
2. arcsin and arctan answer in [−90°, 90°]; arccos in [0°, 180°].
3. Arguments range over the full exact-value set, so arcsin/arctan answers can be negative and arccos answers can exceed 90°.