From Förberedande kurs i matematik 1

In the polynomial \displaystyle 1-x^{2}, only the second term depends on x and, on account of the minus sign in front of that term, the whole expression is largest when the square x² is least. The quadratic term x² is least when \displaystyle x=0. The polynomial's largest value is equal to \displaystyle 1-0^{2}=1\,.