To show this they use the following corollary to the theorem by Obreschkoff of 1920-1923 mentioned earlier; that is, the following corollary gives the necessary conditions under which a polynomial with one positive root has exactly one sign variation in the sequence of its coefficients.
The following corollary gives the necessary conditions under which a polynomial with one positive root has exactly one sign variation in the sequence of its coefficients. This is to show this they use the following corollary to the theorem by Obreschkoff of 1920-1923 mentioned earlier; that is.