We can find the angular dispersion by calculating \(d \theta\) and \(d \lambda\), for finding \(d\theta\) we have to take the difference of \(\theta_{1}\) and \(\theta_{2}\) , here \(\theta_{1}\) and \(\theta_{2}\) are angles for end points of a particular color which is having a certain width similarly we can calculate the \(\lambda_{1}\) and \(\lambda_{2}\) using grating equation.