Either enter an exact answer in terms of pi or use 3.14 for pi and enter your answer as a decimal

Express the following as a function of a single angle. cos(60) cos(-20) - sin(60) sin(-20)

Hi, can anyone show me how to do this problem? 100 points for this. in advance

Perry observes the opposite parallel walls of a room in how many lines do the plains containing the walls intersect