Which of the following are situations that can be modeled with a quadratic fuction? select all that apply

The first-serve percentage of a tennis player in a match is normally distributed with a standard deviation of 4.3%. if a sample of 15 random matches of the player is taken, the mean first-serve percentage is found to be 26.4%. what is the margin of error of the sample mean? a. 0.086% b. 0.533% c. 1.11% d. 2.22%

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

Precalculus question, image attached.