Area of the Opening of a 12.2 inch diameter round duct

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

Does the problem involve permutations or? combinations? do not solve. the matching section of an exam has 4 questions and 7 possible answers. in how many different ways can a student answer the 4 ? questions, if none of the answer choices can be? repeated?

Which of the following expressions is equal to 2x^2+8