] as an output (an angle in radian

measure). Let us find some points ( , ) x y using the equation y cos and plot them in the xy -plane. Note that the values of y decrease from p to as x increases from - to . The inverse cosine function is decreasing and continuous in the domain.

By connecting the points by a smooth curve, we get the graph of y cos as shown in Fig. . Fig. .

Fig. . Note (i) The graph of the function y cos is also obtained from the graph y = cos by interchanging x and y axes. (ii) For the function y cos , the x -intercept is and the y -intercept is p .

(iii) The graph is not symmetric with respect to either origin or y -axis. So, y cos is neither even nor odd function. Example . Find the principal value of cos −    Let cos −    = y .

Then, cos y = . The range of the principal values of y cos is , π ] . So, let us find y in , π ] such that cos y = . But, cos π and π ∈ [ , ].

Therefore, y = π Thus, the principal value of cos −    is p . −