導(dǎo)數(shù)非負(fù)或者非正,原函數(shù)單調(diào)遞增或者單調(diào)遞減.單調(diào)減區(qū)間只需要導(dǎo)數(shù)非正,且導(dǎo)數(shù)取零的點(diǎn)可數(shù). 總的來(lái)說(shuō),對(duì)于一般的函數(shù),導(dǎo)數(shù)值非負(fù)且不恒為零就行了. a=-1時(shí),導(dǎo)數(shù)取0的點(diǎn)就只有x=1,不影響原函數(shù)的單調(diào)性.恩 對(duì).a=-1時(shí),函數(shù)單調(diào)遞增. 函數(shù)有單調(diào)減區(qū)間肯定是存在x,使得f'(x)<0. 但是反過(guò)來(lái)說(shuō),f(x)在(a,b)內(nèi)單調(diào)遞減,只需要對(duì)任意x∈(a,b),f'(x)≤0.