Mô tả:
DOÃN XUÂN HUY-THPT Ân Thi-Hưng Yên
PHƢƠNG TRÌNH, HỆ PHƢƠNG TRÌNH, BẤT PHƢƠNG TRÌNH
MŨ VÀ LÔGARÍT
I.Phương trình, bất phương trình mũ :
1/ Đƣa về cùng một cơ số hoặc hai cơ số:
1/ 2
x 2 x 8
13 x
4
;2/ 3
x 1
3
x 2
x 1
x 1
3
x 3
3
x 4
750;3/ 5 .8
x
x 1
x
500 (5.21/ x ) x3 1 x 3; log0,2 2
x 1
x (2; 1) (1; )
x 1
x
5/ 9 x 9 x1 9 x2 4 x 4 x1 4 x2 9 x.91 4 x.21 9/ 4 21/ 91 x log 9 / 4 (21/ 91)
4/( 5 2)
x 1
( 5 2)
x 1
6/ 2 x .4 x 256;7 / 2 x.5x 0,01;8/ 2 x . 3x 216;9/(3 3 3 ) x (1/81)2 x3 ;10/ 2 x.3x1.5x2 12
2
11/ 2
x 2 4
5
x 2
;12/8
x
x2
2 x
36.3 ;13/1 5
x2 x
1/ 2 x 1
25;14/ 2
1/(3 x 1)
2
;15/( 10 3)
x 3
x 1
( 10 3)
x 1
x 3
2/ Đặt ẩn phụ:
1/(7 4 3) x 3(2 3) x 2 0(t 2 3/ t 2 0);2/(3 5) 2 x x (3 5) 2 x x 212 x x 0
2
2
(t 1/ t 2 0);3/ 23 x 6.2 x 1/ 23( x1) 12/ 2 x 1(t 2 x 21 x );4/ 32 x 8.3x
( chia 2 vế cho 32 x ); 5/ 4 x
x 2
2
5.2 x1
x 2
2
7 / 27 x 6.64 x 6.36 x 11.48 x ;8/ 22 x 2 x
2
2
2 x 1
2
2
1
9.2x
2
x
x4
0
24 x1;9/( 5 2 6 ) x ( 5 2 6 ) x 10
2
2
9.9
6 0;6/ 432cosx 7.41cosx 2 0 ;
72 x
2.3x 2 x2
2t 4
1 x
1
x
10 /
6.(0,7)
7;11/
1
1
;12
/
3.
x
x
x
100
3 2
t 1
3
3
13/ 9sin x 9cos x 10;14/ 22 x
x4
2
22 x2 0;15/ 22
x 3 x 6
15.2
x 1
x
12
x 3 5
2x ;16/ 9 x 3x2 3x 9
17 / 25x 10x 22 x1;18/ 4 x 2.6 x 3.9 x ;19/ 4.3x 9.2 x 5.6 x / 2;20/125 x 50x 23 x1 .
3/ Sử dụng tính đơn điệu của hàm số:
1/ 2x 1 3x / 2 ;2/ 2 x1 3x1 6 x 1;3/(2,5) x (0,4)1/ x 2,9;4/ 3
1
x 4
2
2 x 4
13;5/ 2 x 6 x
DOÃN XUÂN HUY-THPT Ân Thi-Hưng Yên
6/ 2x1 2 x x ( x 1)2 ;7 / 2 3 x x2 8 x 14;8/ 3x 6 x10 x2 6 x 6;9/ 3x 5x 6 x 2
10/ 32 x3 (3x 10).3x2 3 x 0;11/ 3.25x1 (3x 7).5x1 2 x 0;12/ x2 (3 2 x ) x 2 2 x1 0
2
2
32 x 3 2 x
13/ 3 3 2 2 6 2 x 6;14/ 2 3 5 2 3 5 ;15/
0.
4x 2
2
2
y
16/ 4sin ( x ) 4cos ( x ) 8 x2 12 x 1/ 2(3/ 4);17 / 4sinx 21sinx cos( xy) 2 0( k ;0)
x
x
x
x
x
2 x 1
2 x 1
2x
x 1
x
x 2
18/ 1 sin2 x.2cos 2 x 0,5.sin2 2 x cos 2 x sin2 x 2sin2 x 212 sin x 0 sin2 x 0;0,5
19/(2 2)
sin2 x
(2 2)
cos 2 x
(2 2)
2
(1 2 / 2)
cos 2 x
cos 2 x
(cos2 x 0);20/ 2
1 x 2
x2
2
12 x
x2
( x 2) / 2 x
4/ Một số dạng khác:
1/ 4 x
2
3 x 2
4x
2
6 x 5
42 x
2
3 x 7
1 (4 x
2
3 x 2
1)(4 x
2
6 x 5
x 1
1) 0;2/( x2 2 x 1) x1 1
3/ 5.32 x1 7.3x1 1 6.3x 9 x1 0 5.32 x1 7.3x1 3x1 1 0;4/( x x2 ) 2 x
2
5 x 2
1
5/ 4x 1.32 x 4.3x 1 0 4.32 x 4.3x 1 (2.3x 1) 2 0(*) BPT vô nghiệm vì x = 0 KTM (*).
2
6/ 4x
2
x
21 x 2( x1) 1;7 / x2 .2 x1 2
2
2
x 3 2
x2.2
x 3 4
2 x1;8/ x2.3x1 x(3x 2 x ) 2(2 x 3x1)
9/ x2 .3x 3x.(12 7 x) x3 8 x 2 19 x 12;10/ 4 x 8 2 x 2 4 ( x 2 x).2 x x.2 x1. 2 x 2
11/ 2 5 x 3x2 2 x 2 x.3x. 2 5 x 3x 2 4 x 2.3x ;12/( x 2 1/ 2) 2 x
13/( x2 4 x) x
15/1/(3
x 1
18/ n x
22/ 72 x
2
10
(4 x) x
2
10
( x 10; 1;4);14/( x 2) x
1) 1/(1 3 );16/( x 1)
n1
x 1
x
2
x2 2 x
3
2
2 x
2
x 1
( x 2 1/ 2)1 x
( x 2)11x20 ( x 1;2;3;4;5)
x 1 ;17 /( x x 1)
2
2
x 3
x 1
( x x 1)
2
x 2
x 5
n 1 x 1( x n; n 1);19/ 3x cosx;20/ x x 5( x5 t );21/ 75 57 x log7 / 5 (log5 7)
n
7 2
x 1
2
5
x
x
nx n(n 0) x 1
II. Phương trình, bất phương trình lôgarít:
1/ Đƣa về 1 cơ số:
1/ log5 x log25 x log0,2 3;2/ 0,5lg (5x 4) lg x 1 2 lg 0,18;3/ log2 x log3 x log4 x log20 x
4/ lg ( x 6) 0,5lg (2 x 3) 2 lg 25;5/ log5 ( x 2 1) log1/ 5 5 log5 ( x 2) 2log1/ 25 ( x 2)
2
DOÃN XUÂN HUY-THPT Ân Thi-Hưng Yên
3
x3 1
3
3
2
3
3
6 /(log 2 x).log3 log3
log 2 x x 1;
;7 / log 1 ( x 2) 3 log 1 (4 x) log 1 ( x 6)
x
8
2
3 2
4
4
4
2
8/ log2 ( x 3) log0,5 5 2log0,25 ( x 1) log2 ( x 1)( 2)9/ log0,5 (1 x / 2) log2 2 x / 4 0(1)
10/ 2log2 ( x 2 1 x) log0,5 ( x 2 1 x) 3;11/ log 2 tanx log 4 cosx /(2cosx sinx) 0
12/ log5 x log5 ( x 6) log5 ( x 2);13/ log5 x log25 x log0,2 3;14/ lg ( x 2 2 x 3) lg ( x 3) /( x 1)
0;15/ 0,5.lg (5 x 4) lg x 1 2 lg 0,18;16/ log2 ( x x 2 1).log3 ( x x 2 1) log6 ( x x 2 1)
17 / log1/ 5 ( x2 6 x 8) 2log5 ( x 4) 0;18/ log2 ( x 3) 1 log2 ( x 1)
19/ 2log8 ( x 2) log1/ 8 ( x 3) 2/ 3;20/ log0,5 x log3 x 1( log3 x(1 log2 3) 1 0 x 3log2 / 3 3 )
20/ log2 x log3 x log5 x log 2 x.log3 x.log5 x;21/ log5 3x 4.log x 5 1;22/ log 2 ( x 2 2).log (2 x ) 2 2 0
23/ log( x3) 6 2log0,25 (4 x) / log2 ( x 3) 1( x 3); log2 x.log3 2 x log3 x.log2 3x 0(0 x 6 / 6; x 1)
2/ Đặt ẩn phụ:
1/1/(4 lg x) 2/(2 lg x) 1;2/ log0,04 x 1 log0,2 x 3 1;3/ 3log x16 4log16 x 2log2 x
4/ log x2 16 log2 x 64 3;5/ lg(lg x) lg(lg x3 2) 0;6/ log 2 (4 x1 4).log 2 (4 x 1) log1/
2
1/8
7 / log(32 x ) (2 x2 9 x 9) log(3 x ) (4 x 2 12 x 9) 4 0;8/ log4 (log2 x) log2 (log4 x) 2( x 4t t 1)
2
9/ log2 x (2/ x).log22 x log24 x 1( (t 1)(t 4 2t 3 t 2 2t 1) 0);10/ log x (125x).log 25
x 1(5 &1/ 625)
11/ log x 3 log3 x log x 3 log3 x 1/ 2;12/ log 2 (4 x 1) log 2 (22 x3 6) x;13/ log x (5 x).log5 x 2
8x
1
2x 1
2x 1
14 / 4 2log 2 1
log
2
log
4
t
4
t
1:
t
log
x 3/ 2
2
2
2
2
2x 1
2
2x 1
(2 x 1)
2
15/ logsin xcosx sinx.log sinxcosxcosx 1/ 4;16/ log x 2.log x /16 2 log x / 64 2;17 / log5 x (5/ x) log5 x 1
18/ log2 x 10log2 x 6 0;19/ lg(6.5x 25.20 x ) x lg 25;20/ 2(lg 2 1) lg(5 x 1) lg(51
21/ log1/ 3 x 5/ 2 log x 3;22/ log x 2.log2 x 2.log2 4 x 1;23/ log x 2.log x /16 2 1/(log2 x 6)
x
5)
24/ log32 x 4log3 x 9 2log3 x 3;25/ log1/2 2 x 4log 2 x 2(4 log16 x 4 )
26/ log2 (2 x 1).log1/ 2 (2 x1 2) 2;27 / log22 x log1/ 2 x 2 3 5(log4 x 2 3)
28/ log x (2 x) log x (2 x3 );29/ 2log5 x 2 log x (1/ 5);30/ 4log2 2 x xlog2 6 2.3log2 4 x ( xlog2 6 6log2 x )
2
3
DOÃN XUÂN HUY-THPT Ân Thi-Hưng Yên
3/ Phƣơng pháp mũ hóa, lôgarít hóa:
log5 5
xlog4 x2 23(log4 x1) ;2/ x(lg x5) / 3 105lg x ;3/ x6 .5log1/ x 5 11
11
;4/ xlg
2
x lg x3 3
2/ ( x 1 1) 1 ( x 1 1) 1
5/ log1/ 3 log4 ( x 2 5) 0;6/ log x log9 (3x 9) 1;7 / log2 x ( x 2 5 x 6) 1;8/ log(3 x x2 ) (3 x) 1
9/ x2log2 2 xlog2 x 1/ x;10/ xlog2 x4 32;11/ xlg
3
14 / log1/ 2log3
2
x 3lg x 1
1000;12/ 6log6 x xlog6 x 12;13/ log x log 2 (4 x 6) 1
2
x 1
x2
x2
x 1
3x 2
0;15/ log 2log1/ 3
log1/ 2log3
;16 / log x6 log 2
0;17 / log x
1
x 1
x2
x2
x
2
x
2
3
18/ log2 log3 (log4 x) 0;19/ log2log2 x log3log3 x( t x 22 33 t log3/ 2 (log3 2))
t
t
2log3log3 2
20/ log2log3 x log3log2 x log3log3 x log2log3 x log3 (log3 x / log 2 x) log3log3 2 x 3
2 log 2 3
log3
2 3
21/ log2log x 3 log3log x 2 log2log3 x log3log2 x log3 (2t log 2 3) t 1 x 3
22/ log2log3log4 x log4log3log2 x( x 4) log3log2 x (log3log 4 x)2 log32t log3 (2t )(t 1)
1 log3 48
3
1 4log3 2 log3 48 log3t 1 log3 48 x 4
24/ 2.x0,5log2 x 21,5log2 x ;25/ log2 x log0,25 ( x 3)
x 4
; 23/ log x ( 9 x 2 x 1) 1
1 ( x 4)log2 log ( x / x 3) 0
4/ Sử dụng tính đơn điệu của hàm số:
1/ x lg( x2 x 6) 4 lg( x 2) x lg( x 3) 4 x 4;2/ log3 ( x 1) log5 (2 x 1) 2 x 2
3/( x 2)log32 ( x 1) 4( x 1)log3 ( x 1) 16 0(log3 ( x 1) 4;4/( x 2) x 80/81;2)
t
4/ log2 (1 x ) log3 x( t 1 3 2t t 2);5/ xlog2 9 x 2.3log2 x xlog2 3 (log 2 x t 9t 12t 3t )
6/ 3log3 (1 x 3 x ) 2log2 x ( x 26t 1 8t 4t 9t t 2);7 / 2log5 ( x3) x log5 ( x 3) log 2 x
t 2t 3 5t x 2;8/ log2 x 3log6 x log6 x x 3log6 x 2log6 x 6t 3t 2t t 1 x 1/ 6
9/ 3log2 x x2 1;10/ 22 x1 232 x 8/ log3 (4 x2 4 x 4)(VP VT , x 1/ 2)
t
t
11/ log7 x log3 ( x 2)(log7 x t t log3 ( 7 2) 3t 7 2 1 f (2) f (t )
( 7 / 3)t 2.(1/ 3)t 2 t log7 x 49 x 0)
12/ 4
2
x 2
2 x 2 2
log 3 ( x 2 2 x 3) 2 x
2
2 x
log1/ 3 (2 x 2 2) 0 2 x
log3 (2 x 2 2) x2 2 x 3 2 x 2 2 x 3
4
2
2 x 3
log3 ( x 2 2 x 3)
DOÃN XUÂN HUY-THPT Ân Thi-Hưng Yên
13/ log2 ( x 2 5x 5 1) log3 ( x 2 5x 7) 2(t x 2 5 x 5 f (t ) log 2 (t 1) log3 (t 2 2) 2
f (1) 0 t 1 1 x (5 5) / 2 (5 5) / 2 x 4
14/ 2
x 2
x 2
log2 (4 x x 2 2) 1 log2 2 ( x 2)2 2 .VT 1 VP x 2
15/ 2log3 cot x log2cosx( t t 1);16/ log2 x log3 ( x 1) log4 ( x 2) log5 ( x 3)
f ( x) log2 x log4 ( x 2) f '( x) 1/ x ln 2 1/( x 2)ln 4 0x 0 f(x) đồng biến khi x > 0.
Tương tự g ( x) log3 ( x 1) log5 ( x 3) cũng đồng biến khi x > 0. Suy ra pt có nghiệm dn x = 2.
16/( x 1)log1/2 2 x (2 x 5)log1/ 2 x 6 0 (log2 x 2) ( x 1)log2 x 3 0 0 x 2 x 4
log5 ( x 2 4 x 11)2 log11 ( x 2 4 x 11)3
17 /
0(t x 2 4 x 11 0; f (t ) 2log5t 3log11t;
2
2 5 x 3x
f '(t ) ln(121/125) / t ln5.ln11 0t 0;0 f (1) x 2 15 x 6
18/ log
2 2 3
( x 2 2 x 2) log(2
3)
( x 2 2 x 3); a 2 3 2; t x 2 2 x 3 0
log2 a (t 1) log a2 t u a 2u 1 (2a)u (a / 2)u (1/ 2a)u 1 u 2 x 1 11 4 3
19/( x 1)log1/2 3 x 2( x 3)log1/ 3 x 8 0;20/ 2 x 2 8x log 2 (2 x 1) /( x 1) 2
2( x 1)2 log2 ( x 1)2 log2 (2 x 1) 2(2 x 1) ( x 1)2 2 x 1 x 0;4
5/ Một số Phƣơng trình, bất phƣơng trình khác:
1/1/ log1/ 3 2 x 2 3x 1 1/ log1/ 3 ( x 1) (0;1/ 2) (1;3/ 2) (5; ) ;2/(2 x 3.2 x ) 2log2 xlog2 ( x6) 1(a 1)
3/ log x ( x 1) lg1,5(0 x 1 VT 0 VP; x 1 VT 1 VP)
4/ log2 ( x2 3 x2 1) 2log2 x 0 0 (t t 2 2)(t 2 3) 1& t 3 2 t 3 1 x 0
5/ log2 (3.2 x1 1) / x 1( x 1 log2 (2/ 3) x 0);6/( x 1) / log3 (9 3x ) 3 1( MS log 3 9 3 0)
7 / log5 x log x ( x / 3) log5 x(2 log3 x) / log3 x((0; 5 / 5) (1;3));8/1/ log 4 ( x 1) /( x 2) 1/ log 4 ( x 3)
III. Hệ phương trình, bất phương trình mũ và lôgarít:
23 x1 2 y 2 3.2 y 3 x
32 x 2 y 77 2 x 2 y 12
23 x 5 y 2 4 y
1/ x
;2 /
;3/ x
;4 /
;
y
x 1
x
2
x
y
5
3
2
7
4
2
y
(2
2)
3x 1 xy x 1
5
DOÃN XUÂN HUY-THPT Ân Thi-Hưng Yên
x 2 2 x 3 log3 5
4 x y 1 3.42 y 1 2(1)
5(log x y log y x) 26
5 y 4 (1)
3
5/
;6 /
;7 /
2
x 3 y 2 log 4 3(2) xy 64
4 y y 1 ( y 3) 8(2)
x y
12
(1 2log xy 2)log( x y ) xy 1
xlog8 y y log8 x 4
xlog 2 3 log 2 y y log 2 x
x y
8/ x+y
;9 /
;10 /
;11/
3
xlog
12
log
x
y
log
y
y
x
3
3
3
log 4 x log 4 y 1
x y 2 3
e x e y (log 2 y log 2 x)( xy 1)
log 22 x log 2 x 2 0(1)
x.2 x y 1 3 y.22 x y 2
12 / 2
;13/
;14 / 3
2 x y
x y
2
2
2
x
.2
3
y
.8
1
x y 1
x / 3 3x 5 x 9 0(2)
( x 1)lg 2 lg(2 x1 1) lg(7.2 x 12)
log1/ 4 ( y x) log 4 (1/ y) 1
x 1 2 y 1
15/
;16 /
;17 / 2
2
2
3
log x ( x 2) 2
x y 25
3log9 (9 x ) log3 y 3
Gợi ý một số bài:
x 2 2 x 3
Bài 5: (1) 3
5 y 3 1 y 3 0 y 3 (2) : 4 y y 1 ( y 3) 2 8
y( y 3) 0 3 y 0 y 3 x 1;3
Bài 6: (2) x y 1 1 2 y log4 3;(1) 2 412 ylog4 3 3.42 y1 (3.42 y1 1)2 0 42 y1 1/ 3
y 0,5log4 (4/ 3); x 2 log4 (9 3 /8)
Bài 14: (1) có nghiệm ( 1; 4 ). Hàm số vế trái của (2) dương trên khoảng ( 1; 4 ) nên hệ có nghiệm là
khoảng ( 1; 4 ).
------------------ // ------------------
6
- Xem thêm -