WHAT IS INVERSE TRIGOMENTRY AND WHATS BENEFIT

in a very simple language , its just opposite to what u do in trigonometry. for example, in trigonometry u find sine of 90⁰ = 1

, in inverse trigo- sine^-1(1) = 90⁰ . 

It mainly helps in finding angles of a triangle (if sides are known) .

in practical considerations:

For angles near 0 and π, arccosine is ill-conditioned and will thus calculate the angle with reduced accuracy in a computer implementation (due to the limited number of digits). Similarly, arcsine is inaccurate for angles near −π/2 and π/2. To achieve full accuracy for all angles, arctangent or a tan2 should be used for the implementation.