...repeated roots. But Girard gave no proof. Descartes, in the third book of La Geometrie, said that an equation can have as many distinct roots as the number of dimensions (degree) of the unknown. He said "can have" because he considered negative roots as false roots. Later,...

...formulated it cautiously: "Every equation can have as many distinct roots (values of the unknown quantity) as the number of dimensions of the unknown quantity in the equation." Girard overcame this psychological difficulty and stated in his New Discoveries in Algebra of 1629...

...subject of impossible roots, Descartes first seems more cautious than Girard (the emphasis is mine): Every equation can have as many distinct roots as...dimensions of the unknown quantity in the equation. [16, p. 159] This at least can be proved by Descartes' preceding observation (see theorem 5.15). However,...