Find the truth set of

The radius of the base of a cylinder is 10 centimeters, and its height is 20 centimeters. a cone is used to fill the cylinder with water. the radius of the cone's base is 5 centimeters, and its height is 10 centimeters.

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

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )