Since we are mainly interested in zeros of the polynomial , it looks like this Demonstration is less general than the so-called depressed equation . But Vieta showed that in the irreducible case, using the substitution gives the equation [2, p. 133].
 D. Kurepa, Higher Algebra, Book 2 (in Croatian), Zagreb: Skolska knjiga, 1965 pp. 1072–1074.
 G. E. Martin, Geometric Constructions, New York: Springer, 1998.