一元二次方程是初中数学的重要内容.巧妙地构造一元二次方程,可以解决许多难度较大的问题.现以几道典型的竞赛题为例,介绍构造一元二次方程的常用方法.一、应用方程根的定义例1若ab≠1,且有5a2+2001a+9=0,9b2+2001b+5=0,则ba的值是().(A)95(B)59(C)-20501(D)-20901(2001年全国 One-member quadratic equation is an important part of junior high school mathematics. Cleverly constructing a one-dimensional quadratic equation can solve many difficult problems. Now we use a few typical competition questions as examples to introduce a common method for constructing a one-dimensional quadratic equation. , the definition of the application of the equation root 1 if ab ≠ 1, and there is 5a2 + 2001a + 9 = 0, 9b2 + 2001b + 5 = 0, then the value of ba is (). (A) 95 (B) 59 (C) -20501(D)-20901 (National, 2001)