The bugle is one of the simplest brass instruments; it is essentially a small horn with no valves. All pitch control is done by varying the player's embouchure, since the bugle has no other mechanism for controlling pitch. Consequently, the bugle is limited to notes within the harmonic series. The bugle is used mainly in the military.
... If the discriminant is negative, then there are two different solutions x, both of which are complex numbers. The two solutions are complex conjugates of each other. ...