Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 5 - No. 2)
When should we use the inverse trigonometric functions?
When you know the sides and need to find the angle.
When you know an angle and two sides, to find the third.
When trying to find the area.
When using the Pythagorean theorem.
Explication
Inverse trigonometric functions are used to find the angle, if you know the sides.