How do I solve this?

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

Which of the following is the true for f(x) = 5cos

Ascientist has 50 grams of a radioactive element. the amount of radioactive element remaining after t days can be determined using the equation (1) after two days the scientist receives a second shipment of 50 grams of the same element. the equation used to represent the amount of shipment 2 remaining after t days is 10) - 50 which of the following is an equivalent form of the expression for the amount remaining in shipment 2? what’s the answer?