An instrument is a concrete or abstract tool intended for a purpose other than mechanical work, in particular a refined one.
Musical instruments are devices designed to produce music, frequently by plucking or striking a string or bell or drum surface, or by forcing air to resonate (see wind instruments).
... x, both of which are real. (Geometrically, this means that the parabola intersects the x-axis in two points.)
If the discriminant is negative, then there are two different ...