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有些题目中的条件是含(或可以化为)一元二次方程,往往不是去解这个一元二次方程,而是把方程适当变形后进行整体代换,从而使问题易于获得解决,它的优点是:省时、省事、思路清晰、目标明确.请看如下几例:1把方程ax~2+bx+c=0(a≠0)的整体作为零值进行代换1.1求式变形后,直接代换例1已知方程x~2-x-5=0,不解方程,求:x~3-2x~2-4x+5的值.分析把求式中每三项进行分组,指数由高到
In some questions, the condition (or can be) into the quadratic equation contains (or can be) a quadratic equation, often not to solve the quadratic equation, but the equation properly deformed after the overall replacement, so that the problem is easy to be solved, its advantages See the following examples: 1 Substitution of the whole of the equation ax ~ 2 + bx + c = 0 (a ≠ 0) as a zero value 1.1 After the deformation of the equation, Direct Replacement Example 1 Known equation x ~ 2-x-5 = 0, do not understand the equation, find: x ~ 3-2x ~ 2-4x +5 value analysis of the formula for each three groups, the index From high to