Logarit Trong De Dai Hoc

<span class='text_page_counter'>(1)</span>ph¬ng tr×nh vµ bÊt ph¬ng tr×nh logarit I) ph¬ng ph¸p mò ho¸ vµ ®a vÒ cïng c¬ sè:. Gi¶i c¸c ph¬ng tr×nh vµ c¸c bÊt ph¬ng tr×nh sau: 5 ¿ log cosx 4 . log cos x 2=1 1) log 1  2 x  x  2   log 3  2x  2  0 2 6 ¿ log 2 ( x-1 ) =2log 2 ( x 3+ x +1 ) 3 7 ¿ log 3 x +log 4 x=log 5 x 1 2 ¿ log 4 {2log 3 [ 1+ log 2 ( 1+3 log 2 x ) ] }= 2 1 3 2 8) log x  8  log x  58  log x  4x  4   2 3 ¿ log 2 ( x − 1 )=log 1 ( x-1 ) 2. . 3. 2. . 2. . . . 2. 4 ¿ log x ( x 2 +4 x − 4 ) =3 3 2 3 3 9 ¿ log 1 ( x +2 ) -3=log 1 ( 4-x ) +log 1 ( x +6 ) 2 4 4 4 10) log 2 ( x 2+ x +1 ) + log 2 ( x 2 − x+ 1 )=log 2 ( x 4 + x 2 +1 ) +log 2 ( x 4 − x 2+ 1 ) 11) 2 ( log 9 x ) 2=log 3 x . log 3 ( √ 2 x +1− 1 ) 12) log 2 ( x 2+3 x +2 ) + log 2 ( x 2 +7 x+12 ) =3+ log 2 3 13) log 2 x+ log 3 x + log 4 x =log 10 x 20) |log 3 x − 2|<1 14) log x ( x +6 ) =3 2 x −3 21) log 3 <1 2 x −3 log ( 1−x 15) x ) 2 =1 22) log 2 log 3|x −3|≥0 16) log ( x +1 )2 +2=log 4 − x+ log ( 4+ x )3. √. 3. 4. √2. √. 3. 8. x+1. x. 17) ( x − 1 ) log5 3+ log 5 ( 3 +3 ) =log 5 ( 11 . 3 −9 ) 18) log 2 ( x 2 −16 ) ≥ log 2 ( 4 x −11 ) 19). 2l o g   x  1 . 5 . 26) ( 0 , 08 )log. x −0,5. x. ≥. 5 √2 2. ( ). x− 0,5. 27) 2( log x ) + x log x 32 1 log 1 x < log 1 ( 1+ √3 x − 1 ) 28) 2 3 3 1 29) log x x − ≥ 2 4 log ( 2 x − 1) 30) 0 , 12log x ≥ 5 √ 3 3 31) |1+log x 2004|<2 2. (. x− 1. ) ( ). x −1. log a ( 35 − x 3 ) >3 log a ( 5 − x ) 33) ( 4 x −12 .2 x + 32 ) log 2 (2 x −1)≤ 0 4 x−2 1 34) log x ≥ |x −2| 2 1 1 > 2 35) log √ 2 x − 3 x +1 log 1 ( x +1 ) 1 32). 2. (. ). 3. 3 3. 36) log 42 x −log 21 x +9 log 2 322 < 4 log 21 x x 2 8 2 2 37) log 1 ( x −6 x +8 )+ 2 log 5 ( x −4 ) >0. ( ). 5. 2. 38) log 1 [ log 4 ( x −5 ) ] > 0 2. 2. 24) log x ( 5 x 2 − 8 x+3 ) >2  l o g  5  x 1 3 x −1 >0 25) log x 2 x +1 log (2 x − 1) 2 −2 HD: 0,08 = 2 = √ 2 = 5 √ 2 25 5 2. 2. 2. x. 23) log 1 [ log 2 ( 3 +1 ) ]> −1. ( ). ( ) ( ). .

<span class='text_page_counter'>(2)</span> 39) log 2 x ( x 2 − 5 x +6 ) <1 x −2. 40) 5log x <1 ( x ) 41) log 3 3 −1 ≥ 1 x−1 1 log 1 ( x −1 ) > log 1 ( 1+ √3 x − 2 ) 42) 2 2 2 ¿ x log z+ z log z =512 y log x + x log y =8 43) log z x + y log z=2 √ 2 ¿{{ ¿ 3. y. y. z. z. z. x. II) phơng pháp đặt ẩn số phụ: 2. 2. lg x −3 lg x−. 9 2. Gi¶i c¸c ph¬ng tr×nh: 3 ¿ log 2 ( 3 x −1 ) . log 2 ( 2. 3 x − 2 )=2 4 ¿ x +lg ( 1+2 x ) =xlg5+ lg6. − 2 lg x. 1¿ x =10 log [ 9 ( x −2 ) ] 2 ¿ ( x-2 ) =9 ( x-2 )3 5 ¿ log2 ( x- √ x 2 −1 ) . log 3 ( x + √ x 2 −1 ) =log 6 ( x- √ x2 −1 ) 3. 6 ¿ lg 2 ( x 2 +1 ) + ( x 2 − 5 ) lg ( x 2+1 ) -5x 2=0 7 ¿ log 2 [ x ( x-1 )2 ] + log 2 ( x 2 − x ) -2=0 8¿ 9¿ 10) 11) 12) 13). 2. 2. √ 3+ log ( x − 4 x+ 5 ) +2 √5-log ( x − 4 x +5 ) =6 2. 2. 2. log 2 x + √ log 2 x +1=1 log 5 ( 5 x −1 ) . log 25 ( 5x+ 1 −5 )=1 ( x − 1 )log [ 4 ( x− 1) ] =8 ( x −1 )3 log 2 ( 5 x −1 ) . log 2 ( 2. 5 x −2 ) =2 3log x +x log 3 =6 14) log 2 2+log 2 4 x =3 2. 2. 2. x 2 2. x. 17) 3log x −18 x. 2 1 2. log3. 1 2. 2 1 2. 2. 3. 2. 15) log x −2 ( x − 1 ) log 2 x +2 x −6 x +5=0 16) log 2 ( 5 x +2 ) +2 log5 +2 2− 3>0 2 3. 18) log 22 x − ( x +1 ) log 2 x +2 x − 2> 0 x 19) log 3 x . log 2 x < log 3 x 2 +log 2 4 log x log x 5 20) 2 +x 2 21) 3( log x ) + x log x 6 3. log 3  4 x  1  log 4 1 3  x. 22) 23). √ 2−|log x|> log 2. 2. 5 2. x. +3>0. III) ph¬ng ph¸p h»ng sè biÕn thiªn: 1) Gi¶i ph¬ng tr×nh: lg 4 x +lg 3 x − 2 lg 2 x − 9 lg x − 9=0 2) Cho ph¬ng tr×nh: lg 4 x + ( 2 m−1 ) lg 3 x+ m ( m −2 ) lg 2 x − ( m2 −m+1 ) lg x − m+1=0 a) Gi¶i ph¬ng tr×nh víi m = -1. b) Xác định m để phơng trình có bốn nghiệm phân biệt. IV) Sử dụng tính đơn điệu (đồng biến hoặc nghịch biến): Gi¶i c¸c ph¬ng tr×nh: 1¿ log 2 x+ √ 2 x +2=2 3 2¿ x =1 2 + √ 1+log 2 x 3 ¿ log 2 ( x 2 − 4 ) + x=log 2 [ 8 ( x+ 2 ) ] 4) log √ 5 ( x2 −2 x − 2 )=log 2 ( x 2 − 2 x −3 ) 4. 2 6 ¿ log 2 x + ( x-5 ) log 2 x-2x +6=0 7 ¿ log 2 ( x +3log x ) =log 6 x log ( x+1 ) 8¿ 2 =x 6. 2. 5) x 2+3 log x =x log 5 9) log 23 x+ ( x − 4 ) log 3 x − x +3=0 2. 2.

<span class='text_page_counter'>(3)</span> log 2 x 2  3x  2  log 1  x  m  x  m  8) Gi¶i vµ biÖn luËn ph¬ng tr×nh:. l o g  x  x  6   x l o g  x  2   4 2. 10) 11) 12) 13) 14). 2log (x +3)=x log 3 ( √ x+2 ) =log 2 ( √ x+1 ) log 3 x=log 2 ( √ x+1 ) log 2 √ 2+√ 3 ( x2 −2 x − 2 )=log 2+√ 3 ( x 2 −2 x −3 ) 5. 16) log 2 ( 1+ √3 x ) =log 7 x. 18) 2 log 6 ( √4 x + √8 x )=log 4 √ x 19) log 7 x=log 3 ( √ x+ 2 ) 2 20) log 3 √ x − x −12 + x ≤ 7 − √ x 2 − x −12 7−x 21) x 2+ ( log 2 x −2 ) x+ log 2 x −3> 0. 2. x 2  3x  2.

<span class='text_page_counter'>(4)</span> 17) ( x+ 3 ) log 23 ( x +2 ) + 4 ( x+ 2 ) log3 ( x +2 ) − 16=0.

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