分式求值问题是初中数学学习中的重点和难点,解答此类问题的关键在于找出已知条件和要求值的式子之间的内在联系,并进行适当的恒等变形.变形的对象可为条件,也可为要求值的式子,变形的方法因题而异,现举例说明,以供同学们参考. The problem of fractional evaluation is the key and difficult point in junior high school mathematics learning. The key to solving such problems lies in finding out the internal relations between the formulas of known conditions and the required values, and making the appropriate equal deformation. Can be conditions, but also for the required value of the formula, the method of deformation due to problems, are examples, for the students reference.