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1、對(duì)數(shù)的運(yùn)算性質(zhì) 1)對(duì)數(shù)的定義:)對(duì)數(shù)的定義: ,請(qǐng)同學(xué)們回顧一下上節(jié)課我們所學(xué)習(xí)的內(nèi)容。請(qǐng)同學(xué)們回顧一下上節(jié)課我們所學(xué)習(xí)的內(nèi)容。一般地,如果一般地,如果 的的b次冪等于次冪等于N, 就是就是 1, 0aaaNabbNalog,那么數(shù),那么數(shù) b叫做叫做以以a為底為底 N的的對(duì)數(shù)對(duì)數(shù),記作,記作 . 2)指數(shù)式與對(duì)數(shù)式的互化指數(shù)式與對(duì)數(shù)式的互化bNNaablog3)重要結(jié)論用公式)重要結(jié)論用公式負(fù)數(shù)與零沒(méi)有對(duì)數(shù);負(fù)數(shù)與零沒(méi)有對(duì)數(shù); 對(duì)數(shù)恒等式對(duì)數(shù)恒等式 1log, 01logaaa.logNaNa,指數(shù)的運(yùn)算性質(zhì):指數(shù)的運(yùn)算性質(zhì):mnmnmnnmnmnmnmnmaaRnmaaRnmaaaaaa
2、)4();,()(3();,()2( ;) 1 ( M(任意給出)(任意給出)603.14162023150.3567N (任意給出)(任意給出)322.71830.785656.89lgM lgN lgM+lgN lgM-lgN lg(MN) lg lgMlgN lg(M+N)lg(M-N)NMlglgnmlgmnlgNMM(任意給出)(任意給出)603.14162023150.3567N (任意給出)(任意給出)322.71830.785656.89lgM 1.77820.49725.3060-0.4477lgN 1.50510.4343-0.10481.7550lgM+lgN 3.283
3、30.93155.20121.3073lgM-lgN 0.27310.06295.4108-2.2027lg(MN) 3.28330.93155.20121.3073 lg 0.27310.06295.4108-2.2027lgMlgN 2.67630.2159-0.5561-0.78561.00441.1448-50.6308-0.2551lg(M+N)1.96380.76795.30601.7578lg(M-N)1.4471-0.37345.3060出錯(cuò)信息出錯(cuò)信息56.90081.35154.1684-25.469756.90081.35154.1684-25.4697NMlglgnml
4、gmnlgNMM(任意給出)(任意給出)603.14162023150.3567N (任意給出)(任意給出)322.71830.785656.89lgM 1.77820.49725.3060-0.4477lgN 1.50510.4343-0.10481.7550lgM+lgN 3.28330.93155.20121.3073lgM-lgN 0.27310.06295.4108-2.2027lg(MN) 3.28330.93155.20121.3073 lg 0.27310.06295.4108-2.2027lgMlgN 2.67630.2159-0.5561-0.78561.00441.448
5、-50.6308-0.2551lg(M+N)1.96380.76795.30601.7578lg(M-N)1.4471-0.37345.3060出錯(cuò)信息出錯(cuò)信息56.90081.35154.1684-25.469756.90081.35154.1684-25.4697NMlglgnmlgmnlgNMM(任意給出)(任意給出)603.14162023150.3567N (任意給出)(任意給出)322.71830.785656.89lgM 1.77820.49725.3060-0.4477lgN 1.50510.4343-0.10481.7550lgM+lgN 3.28330.93155.2012
6、1.3073lgM-lgN 0.27310.06295.4108-2.2027lg(MN) 3.28330.93155.20121.3073 lg 0.27310.06295.4108-2.2027lgMlgN 2.67630.2159-0.5561-0.78561.00441.448-50.6308-0.2551lg(M+N)1.96380.76795.30601.7578lg(M-N)1.4471-0.37345.3060出錯(cuò)信息出錯(cuò)信息56.90081.35154.1684-25.469756.90081.35154.1684-25.4697NMlglgnmlgmnlgNMM(任意給出)
7、(任意給出)603.14162023150.3567N (任意給出)(任意給出)322.71830.785656.89lgM 1.77820.49725.3060-0.4477lgN 1.50510.4343-0.10481.7550lgM+lgN 3.28330.93155.20121.3073lgM-lgN 0.27310.06295.4108-2.2027lg(MN) 3.28330.93155.20121.3073 lg 0.27310.06295.4108-2.2027lgMlgN 2.67630.2159-0.5561-0.78561.00441.448-50.6308-0.255
8、1lg(M+N)1.96380.76795.30601.7578lg(M-N)1.4471-0.37345.3060出錯(cuò)信息出錯(cuò)信息56.90081.35154.1684-25.469756.90081.35154.1684-25.4697NMlglgnmlgmnlgNMM(任意給出)(任意給出)603.14162023150.3567N (任意給出)(任意給出)322.71830.785656.89lgM 1.77820.49725.3060-0.4477lgN 1.50510.4343-0.10481.7550lgM+lgN 3.28330.93155.20121.3073lgM-lgN
9、0.27310.06295.4108-2.2027lg(MN) 3.28330.93155.20121.3073 lg 0.27310.06295.4108-2.2027lgMlgN 2.67630.2159-0.5561-0.78561.00441.448-50.6308-0.2551lg(M+N)1.96380.76795.30601.7578lg(M-N)1.4471-0.37345.3060出錯(cuò)信息出錯(cuò)信息56.90081.35154.1684-25.469756.90081.35154.1684-25.4697NMlglgnmlgmnlgNM對(duì)數(shù)的運(yùn)算性質(zhì)對(duì)數(shù)的運(yùn)算性質(zhì)兩個(gè)正數(shù)的積的
10、對(duì)數(shù)等于這兩個(gè)正數(shù)的對(duì)數(shù)和兩個(gè)正數(shù)的積的對(duì)數(shù)等于這兩個(gè)正數(shù)的對(duì)數(shù)和兩個(gè)正數(shù)的商的對(duì)數(shù)等于這兩個(gè)正數(shù)的對(duì)數(shù)差兩個(gè)正數(shù)的商的對(duì)數(shù)等于這兩個(gè)正數(shù)的對(duì)數(shù)差logloglogaaaMNMN logloglogaaaMMNN (2)loglog()naaMnM nR(3)語(yǔ)言表達(dá)語(yǔ)言表達(dá):一個(gè)正數(shù)的一個(gè)正數(shù)的n次方的對(duì)數(shù)等于這個(gè)正數(shù)的對(duì)數(shù)次方的對(duì)數(shù)等于這個(gè)正數(shù)的對(duì)數(shù)n倍倍如果如果 a 0,a 1,M 0, N 0 有:有:證明:設(shè) ,logpMa,logqNa由對(duì)數(shù)的定義可以得: ,paM qaN qpaaqpaqpNMa log即證得 NMlogloglogaaaMMNN證明證明:aaaMloglog
11、Mlog NN證明:設(shè) ,logpMa由對(duì)數(shù)的定義可以得: ,paM npnaMnpMna log即證得 naalog Mnlog M(nR)loglognaaMnM證明證明:對(duì)數(shù)運(yùn)算公式幾個(gè)注意點(diǎn):1) 簡(jiǎn)易語(yǔ)言表達(dá)簡(jiǎn)易語(yǔ)言表達(dá):“積的對(duì)數(shù)積的對(duì)數(shù)=對(duì)數(shù)的和對(duì)數(shù)的和”2)真數(shù)的取值必須是真數(shù)的取值必須是(0,)3)有時(shí)公式可以可逆有時(shí)公式可以可逆4)5)log ()aMNloglogaaMNlog ()aMNloglogaaMNnma)(lognamlog例1 計(jì)算(1) (2) )42(log7525lg 100講解范例講解范例 解 :)42(log752522log724log522lo
12、g1422log=5+14=19解 :21lg1052lg105255lg 100例例2 計(jì)算計(jì)算(1) (2) 50lg)2(lg)5(lg2解 (1)(2)原式=18lg7lg37lg214lg) 15)(lg2(lg)5(lg50lg)2(lg)5(lg222lg5lg)2(lg)5(lg22lg)2lg5)(lg5(lg12lg5lg)23lg(7lg) 3lg7(lg2)72lg(22lg3lg27lg3lg27lg27lg2lg0法二法二:原式原式=18lg7lg)37lg(14lg201lg18)37(714lg2練習(xí)練習(xí) (1) (4) (3) (2) 1.求下列各式的值:15log5log332lg5lg 31log3log553log6log2236log2)25lg( )313(log5155log32log2110lg11log50133log12. 用lg,lg,lg表示下列各式:練習(xí)練習(xí) (1) (4) (3) (2) )lg(xyzzxy2lgzxy3lglglglg;zyx2lglglglg;lglg 21lg; zyxlglg2lg21