A set that is not convex is called a non-convex set. A polygon that is not a convex polygon is sometimes called a concave polygon, and some sources more generally use the term concave set to mean a non-convex set, but most authorities prohibit this usage.
In either case you don't need to deal with the absolute value. A rectified sine wave is a periodic signal with a period equal to half of the full sinusoid, I would write the sine in exponential form and integrate over one period to find the series coefficients.
The problem may be more clearly thought of as y = 2(-sin x). This graph is a reflection in the x-axis of the graph y = 2 sin x. The amplitude of 2 tells us that the graph will have a vertical stretch. How to use your TI-83+/84+ graphing calculator for graphing sinusoidal functions. Click calculator. sine wave, or sinusoid, is the graph of the sine function in trigonometry. A sinusoid is the name given to any curve that can be written in the form (A and B are positive).