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分式求值是初中数学竞赛中的一个重要内容,在解题时务必仔细观察题目特点,若能采用灵活的解法,可起到事半功倍的作用.下面举例说明一般的解法.以供同学们学习时参考.一、参数法例1若a/b=3/4,b/c=2/3,c/d=4/5,则(ac)/(b~2+d~2)=____.解设a=3k,则b=4k.由题设可知c=8/3k.d=(10)/3k.∴(ac)/(b~2+d~2)=(3k×8/3k)/((4k)~2+((10)/3k)~2)=(18)/(61).
Fractional evaluation is an important part of junior middle school math competition. When solving problems, we must carefully observe the characteristics of the questions. If we can adopt a flexible solution, we can play a multiplier effect. The following gives an example to illustrate the general solution for students to learn When reference is made to parameter 1, (ac) / (b ~ 2 + d ~ 2) = ____ if a / b = 3/4, b / c = 2/3, c / d = 4/5. The solution set a = 3k, then b = 4k. From the title set we can see that c = 8 / 3k.d = (10) /3k.∴ (ac) / (b ~ 2 + d ~ 2) = (3k × 8 / 3k ) / ((4k) ~ 2 + ((10) / 3k) ~ 2) = (18) / (61).