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.
... to divide by it.)
The symbol
<math>\pm \sqrt {b^2-4ac}</math>
in the formula should be understood as "either of those element(s) of the field whose ...