de Gua's rule

de Gua's rule

[də′gwäz ‚rül]
(mathematics)
The rule that if, in a polynomial equation ƒ(x) = 0, a group of r consecutive terms is missing, then the equation has at least r imaginary roots if r is even, or the equation has at least r + 1 or r- 1 imaginary roots if r is odd (depending on whether the terms immediately preceding and following the group have like or unlike signs).