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).
... two solutions are complex conjugates of each other. (In this case, the parabola does not intersect the x-axis at all.)
Note that when computing roots numerically, the ...