] is called the principal domain of cosine function and the values of

] is called the principal domain of cosine function and the values of cos , −≤ , are known as principal values of the function y cos Fig. . − − − − p p p − p − p − p − p O units y = 4sin θ Inverse - - Inverse Trigonometric Functions From the definition of y cos , we observe the following: (i) y cos if and only if x = cos for −≤ and ≤ π . (ii) cos cos −