众所周知,对于一个实系数的二次三项式 y=ax~2+bx+c(a≠0) ①它的许多性质,诸如:它有无实根,有无有理数根(假定系数为有理数),求根公式,作为二次函数它的正负值区间,在有理数范围内可否因式分解,等等,取决于其判别式 It is well known that for a real coefficient quadratic trinomial y=ax~2+bx+c(a≠0) 1 its many properties, such as: whether it has real roots, whether or not there are rational roots (assuming the coefficients are rational numbers) , find the root formula, as the quadratic function of its positive and negative range, can be factorized in the range of rational numbers, and so on, depending on its discriminant