Arcsine of sine of a quantity is the same quantity back again. So
Note that the notation
From the crests of #y = sin x, 1 = sin (pi/2) = sin ((5/2)pi) = sin ((9/2)pi) = ...# How do you evaluate #sin^(-1) sin (pi/2), sin^(-1) sin ((5/2)pi), sin^(-1) sin ((9/2)pi), ...?#