4.3對(duì)數(shù)

4.3.1對(duì)數(shù)的概念抽象背景，引入概念以2為底5的對(duì)數(shù)以2為底9.3的對(duì)數(shù)以4為底21的對(duì)數(shù)x是以a為底N的對(duì)數(shù)對(duì)數(shù)：logarithm對(duì)數(shù)源于指數(shù).——?dú)W拉一、對(duì)數(shù)的概念1.對(duì)數(shù)的定義：一般地,若ax=N(a>0且a≠1),則數(shù)x叫做以a為底N的對(duì)數(shù),

記作x=logaN(a>0且a≠1,N>0).

其中a叫做對(duì)數(shù)的底數(shù)，N叫做真數(shù).如：若42=16，則2=log416，讀作2是以4為底16的對(duì)數(shù).對(duì)數(shù):logarithm2.對(duì)數(shù)的意義：表示指數(shù)式中的指數(shù)，減輕思維和運(yùn)算負(fù)擔(dān)；ax=N

x=㏒aN.

（a>0,且a≠1）底數(shù)冪真數(shù)指數(shù)對(duì)數(shù)對(duì)數(shù):logarithm指數(shù)與對(duì)數(shù)的聯(lián)系對(duì)數(shù)和指數(shù)運(yùn)算互為逆運(yùn)算很重要！對(duì)數(shù)的種類與特列對(duì)數(shù):logarithm①loga1=；logaa=；01②真數(shù)N>0：負(fù)數(shù)和0沒(méi)有對(duì)數(shù)對(duì)數(shù)的性質(zhì)③alogaN＝N.對(duì)數(shù):logarithm記筆記鞏固概念：指對(duì)互化總結(jié)：底數(shù)不變，冪與真數(shù)互換對(duì)數(shù):logarithm鞏固概念：指對(duì)求值對(duì)數(shù):logarithm鞏固概念：方程與不等式對(duì)數(shù):logarithm[練習(xí)1]求下列各式中x的值.(1)log3(lgx)=1(2)log2(logx

16)=2課后作業(yè)1.課時(shí)作業(yè)P2262.作業(yè)本：課本P123練習(xí)T2、3對(duì)數(shù):logarithm4.3.2

對(duì)數(shù)的運(yùn)算課前回顧定義延伸N對(duì)數(shù)恒等式573問(wèn)題情境對(duì)數(shù)的運(yùn)算性質(zhì)探索發(fā)現(xiàn)1記筆記(真數(shù))積的對(duì)數(shù)=對(duì)數(shù)的和(真數(shù))商的對(duì)數(shù)=對(duì)數(shù)的差換底公式探索發(fā)現(xiàn)2對(duì)數(shù)換底公式換底公式推論記筆記換底公式的應(yīng)用對(duì)數(shù)換底公式的靈活運(yùn)用一思路：底換為6思路：底換為18對(duì)數(shù)換底公式的靈活運(yùn)用二思路:a=?b=?已知指數(shù)連等式時(shí)，可化為對(duì)數(shù)式,或同時(shí)取同底對(duì)數(shù)對(duì)數(shù)換底公式的靈活運(yùn)用二課后作業(yè)

P126-第3題(3)~(6)