我们知道,若二次函数j(劝=。2十b,+c(a并0)与x轴的交点坐标分别为(二1,o),(、2,O)(*1二2),贝巧有 (i)当ao日寸,f(、)0得二“、,或二二,;f(x)0骨二,二,2· (ii)当。0时,f(,)0骨二,,二2;f(x)o份%x,,或二凡· 利用这个常见结论,我们可以解决一类二次函数值符号判定 We know that if the quadratic function j (discussed = 2 b b, +c (a and 0) and the x-axis coordinate coordinates are (2 1, o), (, 2, O) (*1 二 2) , Qiao Qiao has (i) when ao day inch, f (,) 0 has two ",, or two two,; f (x) 0 bone two, two, 2 (ii) when. 0, f (, ) 0 bone two,, two 2; f (x) o share% x,, or two Fan · Using this common conclusion, we can solve a class of quadratic function value symbol decision