【摘 要】
：
求一元二次方程中字母系数的值(或范围)的题型,在近几年各地中考试题中出现较多,稍不注意就会出现这样或那样的错误. 一、既要根据条件求出字母的值,又要用判别式检验有无实
论文部分内容阅读
求一元二次方程中字母系数的值(或范围)的题型,在近几年各地中考试题中出现较多,稍不注意就会出现这样或那样的错误. 一、既要根据条件求出字母的值,又要用判别式检验有无实根 例 1 已知关于x的方程x2-2mx+(m2-4m+5)=0的两个实根x1、x2,且 x1+x2=x1x2,求m的值.(1998年盐城市中考题) 解∵x1+x2=2m,x1x2=m2-4m+5,x1+x2=x1x2. ∴2m=m2-4m+5,得m1=5,m2=1. 当m=5时,原方程为x2-10x+10=0,△>0.m=5(适合),当m=1时,原方程为x2-2x+2=0,△<0.∴m=1(不适合).∴m=5.
The question type for the value (or range) of the letter coefficient in a quadratic equation has appeared in many examination questions in various places in recent years, and one or more mistakes will occur if one does not pay attention. The value of the letter, but also the use of discriminants to test whether there are real roots Example 1 Known about x x2-2mx + (m2-4m +5) = 0 two real roots x1, x2, and x1 + x2 = x1x2, Find the value of m. (1998 Yancheng examination questions) Solution ∵x1+x2=2m,x1x2=m2-4m+5,x1+x2=x1x2. ∴2m=m2-4m+5, get m1=5,m2 =1. When m=5, the original equation is x2-10x+10=0 and △>0.m=5 (suitable). When m=1, the original equation is x2-2x+2=0, △< 0. ∴m=1 (not suitable). ∴m=5.
其他文献
<正> L[-1,1]p denotes the class of Lp-integrable functionson [-1,1]for 1≤P<∞, L[-1,1]∞ = C[-1,1] is the set of continuous functions on (-1, 1)En（f）p is the bes
<正> Ⅰ. INTRODUCTION Let f（ζ） be the analytic and schhcht function in the unit disc U={ζ:|ζ|<1}, ζ1,ζ2 be any points in U, and f（ζ1） · f（ζ2） ≠ 1. We den
<正> One of the features of the rare earth elements is that their 4f electronic shells are unfilled, and their physio-chemical properties also depend on this in
<正> Ⅰ. INTRODUCTION It is well known that the characteristic function of an infinitely divisible distribution F(x) can be written as
<正> Hematite, a common oxide of iron, transits from antiferromagnetic to weak ferromagnetic phase, In this transition, i. e. Morin transition the direction of
<正> During the Late Carboniferous Taiyuan and Shanxi stage, some relevant factors in the formation and distribution of the high-seam zone in Shanxi can be summ
<正> The strueture generator and substructure search computer program (SGSSp) has been used in identification of molecular struclures. It can generate all struc
<正> Theorem 1. Let f（x1,x2,…, xm） be a function of m variables, which has 2-order partial derivative on the origin. Put
<正> Since 1977 ab initio MO calculation has been undertaken in Peking University. Some works have been finished and published, for example, on the study of ele
相传女祸补天时费了九牛二虎之力,在数学世界里,同样需要我们采取“挖”、“补”的方法,并须慎之又慎,稍一疏忽,就会产生错解.下面举例说明. 例题已知复数w=(3-z)/(3+z)(z