Stridulation is the production of sounds by rubbing two parts of the body together; this mechanism is best known in crickets, grasshoppers, and cicadas. Larval Lucanidae, Passalidae[?], and Geotrupidae[?] also stridulate, rubbing a series of ridges on the coxa of the middle legs with a scraper on the trochanter of the hind leg.
... is not 2. (In a field of characteristic 2, the element 2a is zero and it is impossible to divide by it.)
The symbol
<math>\pm \sqrt {b^2-4ac}</math>
in ...