Concept Check In later chapters we will study trigonometric functions of angles othe...

Concept Check In later chapters we will study trigonometric functions of angles other than quadrantal angles, such as and so on. To prepare for some important concepts, provide conjectures in Exercises 103–106. Be sure that your calculator is in degree mode.

With your calculator determine cos 20° and cos(-20°). Make a conjecture about the cosines of an angle and its negative, and test your hypothesis with other angles. (Note: This relationship will be discussed in detail in Section 5.1.)