一、辨别一元二次方程例 1　方程x4+ax3-x2 +a2 -1 =0是否是一元二次方程 ?如果是 ,指出各项系数 ;如果不是说明理由 .解　当x为常数时 ,此方程是关于a的一元二次方程 ,化为一般形式是a2 +x3a+x4-x2 -1 =0 ,其中二次项系数为 1 ,一次项系数为x3,常数项为x4-x2 -1 .二、判别根的 I. Identify the quadratic equation Example 1 Is the equation x4+ax3-x2 +a2 -1 =0 equal to a one-member quadratic equation? If yes, indicate the coefficients; if not explain why. Solution When x is a constant, the equation It is a quadratic equation about a, and it is generalized as a2 +x3a +x4-x2 -1 = 0, where the quadratic coefficient is 1, the linear coefficient is x3, and the constant term is x4-x2 -1 . Root discrimination