判断函数增减性时：常有形如“增+增=增，增－减=增”之类形式，还有什么？请帮我总结出来！ 用定义判断函数增减性，有什么技巧
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f(x)*g(x)，不一定，要求导算一算，例如x*x，都为增函数，但是相乘以后就分区间为增或减函数
增+增=增，增-减=增，减+减=减
减+减=减 减-增=减
还有增-增和减-减是不能判断的
这是复合函数当中判断增减性的性质
判断复合函数的单调性的步骤如下：
(1)
求复合函数定义域；
(2)
将复合函数分解为若干个常见函数（一次、二次、幂、指数、对数函数）；
(3)
判断每个常见函数的单调性；
(4)
将复合函数的定义域分段（每个常见函数在每段定义域上具有单调性）；
(5)
根据“通增异减”求出复合函数的单调性。
复合函数，同增异减。其他的要看情况
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