The function is a Bijection, as for every "x" there is one n only one value of "y"....
And its inverse is rightly (x-sinx)...
if ƒ is the function
then ƒ is one-to-one, and therefore possesses an inverse function ƒ−1. There is no simple formula for this inverse, since the equation y = x + sin x cannot be solved algebraically for x.
But answer is x-sinx as it was well explained by above people.