几道对数题目
\u51e0\u9053\u5bf9\u6570\u7684\u8fd0\u7b97\u7684\u9898\u76ee1 用对数的性质，分子等于以m 为底，真数为2a/2b,分母为以m为底，真数为a/b,值为12、分子分母均换成以3为底的对数，分子为log 3 16/log3 27,分母为log3 8,然后16=2*8,273^3,整理的4/93、x<34、x<-4/3
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1 logm(2a)-logm(2b）=logm(2a/2b）=logm(a/b); logm(a）-logm(b)=logm(a/b)所以原式=【logm(a/b)】/【logm(a/b)】=12 log27(16)=log(3^3) (2^4)=4/3 log3(2); log3(8）=3log3(2）所以原式=【4/3 log3(2)】/【3log3(2）】=4/93 X<34 X>-4/3
绛旓細涓よ竟閮介櫎浠3 涔熷氨鏄2鐨勶紙x鐨勫钩鏂+4锛夋骞=256 256绛変簬2鐨8娆″箓 涔熷氨鏄x鐨勫钩鏂+4=8 x鐨勫钩鏂=4 x=2
绛旓細鏈涢噰绾
绛旓細n鈮8.84 瑙ｏ細2=(1.04)^(2n)ln2=2nln1.04 n=ln2/(2ln1.04)浣跨敤璁＄畻鍣ㄨ绠 n鈮8.84
绛旓細绗竴棰橈紝鏍规嵁瀵规暟鐨勫姞娉曡繍绠楁硶鍒欙紝lg2+lg5=lg锛2*5锛=lg10=1 鎵浠g5=1-lg2=0.699 绗簩棰樺厛閫氬垎鍖栫畝锛屽湪鍋
绛旓細绗竴棰樺垎瀛愬垎姣嶉氫箻浠鐨剎娆℃柟,鐒跺悗浠ｅ叆璁＄畻绗簩棰樼瓑浜-3;log5鐨勬牴鍙2寮鎴1/2涔樹互log5鐨2娆;log49鐨81娆″彉鎴恖og(7鐨勫钩鏂)鐨(9鐨勫钩鏂),鍗崇瓑浜巐og7鐨9娆;log25鐨1/3鍙樻垚1/2涔樹互log5鐨1/3娆,log7鐨勬牴鍙4寮3娆″彉鎴1/3涔樹互log7鐨4娆.绾︾畝杩囩▼浣犲簲璇ユ噦鍚,鏈鍚庡叏閮ㄥ彉鎴-3涔樹互log3鐨2娆...
绛旓細瑙ｅ涓嬪浘鎵绀
绛旓細绗竴棰:2673=11*3^5(琛ㄧず3鐨5娆℃柟)lg2673=lg(11*3^5)=lg11+5lg3 lg11=lg2673-5lg3=1.0415 绗簩棰:Y=(3X-1)^(1/2)+(1-3X)^(1/2)+9 (浣犳槸杩欎釜鎰忔濆惂,濡傛灉鎴戞病鏈夌悊瑙ｉ敊)瑕佷娇鏍瑰彿(3X-1)鍜屾牴鍙(1-3x)鍚屾椂鏈夋剰涔,鍗 3x-1>=0涓1-3x>=0 瑙ｅ緱x=1/3 鍒欏彲寰梱=9 ...
绛旓細涓や釜绛夊紡涓よ竟閮藉彇瀵规暟寰梮lg5.4=lg3,ylg0.6=lg3 鍒1/x+1/y=(lg5.6-lg0.6)/lg3=(lg(28/3))/lg3
绛旓細(1) 鐢辨崲搴曞叕寮忓緱鍒 log14^7=ln7/ln14=ln7/(ln2+ln7)=a; 鏁 ln7=aln2+aln7; 瑙ｅ緱 ln7=aln2/(1-a);14^b=5.鏁 log14^5=b.鍗 ln5/(ln2+ln7)=b;ln5=b(ln2+ln7)=bln7/a=bln2/(1-a);鎵浠 log35^28=ln28/ln35=(2ln2+ln7)/(ln5+ln7)=(2ln2+aln2/(1-...
绛旓細an+2SnS(n-1)=0銆(n澶т簬绛変簬2)an=-2SnS(n-1)an=Sn-S(n-1)-2SnS(n-1)=Sn-S(n-1)涓よ竟鍚岄櫎浠-SnS(n-1),寰 2=1/Sn-1/S(n-1)鎵浠,{1/Sn}鏄叕宸负2鐨勭瓑宸暟鍒,S1=a1=1/2 1/S1=2 1/Sn=n(n+1)Sn=1/n(n+1)n=1鏃,a1=1/2 n>1鏃,鏈:an=Sn-S(n-1)=1/...
