Trig Section 5.1: Graphing the Trigonometric Functions / Unit Circle MULTIPLE CHOICE. Solve the problem. 1) What is the domain of the cosine function? 1) A) all real numbers, except integral multiples of (180 °) B) all real numbers C) all real numbers, except odd multiples of 2 (90 °) D) all real numbers from - 1 to 1, inclusive