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 time period of oscillation of a wave is defined as the time taken by any element of the string to complete one such oscillation. For a sine wave represented by the equation y (0, t) = -a sin(Ït), the time period is given mathematically as T = 2Ï/Ï. Frequency. The frequency of a sinusoidal wave can be defined as the number of complete oscillations made by any element of the wave per unit time. For a sinusoidal wave represented by the equation y (0,t) = -a, frequency of the wave is given by, Its unit is Hertz abbreviated as Hz. One Hertz is equal to one complete oscillation taking place per second.