That will be, if to increase a cosine on a sine?

In someone an inquisitive mind... Woke up If sine of corner alpha to increase on the cosine of corner alpha, a number, equal to the half of sine two alpha, will ensue. This statement hatches from the functions of multiple corners, where sine two alpha equals the doubled product of sine alpha on a cosine alpha. The picture of this trigonometric miracle I will show later:)