Cos(2x) refers to the cosine function with an argument that is twice the input angle x. It produces values between -1 and 1.
A function that combines two or more functions by using one as an input for another. In this case, cos(2x) uses 2x as its input for evaluating cosine.
Even Function: A type of symmetry where f(-x) = f(x) for all x in the domain. Cosine is an even function because cos(-θ) = cos(θ).
Phase Shift: A horizontal shift in the graph of a periodic function like cosine caused by modifying its argument (in this case, doubling x).