同学们知道,在解数列的求值问题时,设未知数很重要.如果设得巧,常会使解题过程简捷,提高解题效率.否则,会加大计算量、增加解题难度.但是,对于“巧法妙解”也要审慎处之,以免弄巧成拙. 譬如:当三个数成等差数列,它们的和为已知数时,常设这三个数为a-d,a,a+d; 当三个数成等比数列时,如果它们的积为 The students know that when solving the problem of number evaluation, it is very important to set the unknown number. If it is well-designed, it will often make the problem-solving process simpler and more efficient. Otherwise, it will increase the amount of calculation and increase the difficulty of solving problems. However, For “a clever trick”, we must be cautious in order to avoid self-defeating. For example, when three numbers are in series and their sum is a known number, these three numbers are ad, a, a+d. When three numbers are proportional, if their product is