Descartes' Rule of Signs

Let P be be a polynomial function with real coefficients and with the terms arranged in order of decreasing powers of x

1. The number of positive real zeros of P is equal to the number of variations in the sign of P(x), or to that number decreased b an even integer.

2. The number of negative real zeros of P is equal to t he n umber of variations in sign of P(-x), or to that number decreased by an even integer.