一元二次方程ax~2+bx+c=0有实数根的条件是判别式△≥0,若其两根为x_1和x_2,那么根据求根公式x=b±b~2-4ac~(1/b~2-4ac)/2a,易得出x_1+x_2=-b/a,x_1x_21=c/a,利用上述关系构造出相应的不等式或不等式组,可求出方程中字母系数的取值范围,根的取值范围,以及字母系数间的关系等问题.这些问题,不仅可考查同学们的基础知识掌握的情况,更能考查同学们的综合应用能力.下面举例加以说明,供 The condition of the quadratic equation ax~2+bx+c=0 with a real number root is the discriminant Δ≥0. If the two are x_1 and x_2, then the root formula is x=b±b~2-4ac~( 1/b~2-4ac)/2a, it is easy to get x_1+x_2=-b/a, x_1x_21=c/a, use the above relationship to construct the corresponding inequality or inequality group, and you can find the letter coefficient in the equation. The range of values, the range of values ​​of the roots, and the relationship between letter coefficients. These questions can not only examine the basic knowledge of the students, but also examine the comprehensive application capabilities of the students. The following examples illustrate that