Modern classical music is music written in the 20th century and beyond. Although much of it draws heavily on earlier forms, modern composers also experimented with rejection of long-held ideas; notably, Arnold Schoenberg questioned the traditional notions of harmony with his twelve-tone system[?], and John Cage questioned the very definition of music with his use of chance and found sounds.
... formula expresses the explicit solution(s) x to the quadratic equation
<math>ax^2+bx+c=0</math>
in terms of the coefficients a, b and c, which are assumed ...