Write the expression as the sine, cosine, or tangent of a double-angle. Then find the exact value of the expression. cos 2120 - sin 2120 Which expression is cos - 120" - sin 120 equal to? Select the correct choice below and fill in the answer box within your choice. (Simplify your answer. Type your answer in degrees. Use integers or decimals for any numbers in the expression.) O A. cos 120 - sin 120 = cos O B. cos 2120 - sin 2120 = tan O O C. cos 2120 - sin 2120 0 = sin