7/25/2019 Tai Lieu 6

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Dang 6: Dang đă   t hi ân phu:

 Phương phap: Dung hai ân ph đê chyên v h   phương trnh. T h   phương trnhgii đưc hai ân ph, t đ gii ra ân c!a phương trnh "an đ#.

Cc v du:$% & '( )ii phương trnh(

**' *+ * * ' * ' x x x x x− + − = − − + +-( * x ≥  -/  t( '0 *0 , 1u x v x u v= + = − ≥

T đ 2y ra( ( ) ( )* * *

* . 0 *' *+ 3 ' '+ * ' 3 '+ '. x x u v x x x u v− − = − = + + − − = + −  Ta c( * *3 '+ ' ' * 1u v uv v u+ − − + − =  

( ) ( )* 4 ' 4 + ' 1u v u v⇔ − − − + =  * 4 ' 14 + ' 1u v

u v

− − =⇔

− + =.

5 $6i * 4 'u v= + , c(

* ' 4 * ' 7 7 '8 3 * 3 * *' + 4. x x x x x x x x+ = − + ⇔ + = − + − ⇔ − = − ⇔ =  

5 $6i 4 + 'u v= − , c(*,8

4 ' ' + * 4 ' 9 41 .37

 x x x x x+ + = − ⇔ + = − ⇔ =  

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7/25/2019 Tai Lieu 6

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:hương trnh c nghi  ;(*,8

4037

 x x= = .

$% & *( )ii phương trnh( * *7 + ' * ' 4 x x x x x+ + − − + = −

-(''07

 x x≤ − ≥ − .

-/  t( * *7 + '0 * 'u x x v x x= + + = − + .

Ta c( * *u v u v− = −

( ) ( )' 1

'

u v u vu v

u v

⇔ − + − ==

⇔+ =

 

T đ ta đưc' 7

04 ,

 x x= = .

$% & 4( )ii phương trnh(*4 * ' 3 7 * 7 8 1 x x x x+ − + + + + + =  

-('*

 x ≥ − . -/  t( * '0 7.u x v x= + = +  

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7/25/2019 Tai Lieu 6

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Ta c(* * ** 8

1.44 3 8 1

u vv u x

u vu v uv

   

=− =⇔ ⇔ =

+ =− + + = 

Bi t   p t!"ng t#:

)ii c<c phương trnh 2a(

'= 4* 4 * 4 3 + 9 1 x x− + − − =   -( * x = −  

*= 4* 4 * 4 3 + '3 1 x x− − − + =   -( * x = −

4= * *'8 '8  x x x x+ − + − =   -( '0 7 x x= =

7= *

' ' ** x  x

+ =−

  ->( ' +'0*

 x x  − ±

= =

+= ( ) ( ) ( ) *7 ' * '1 4 9 x x x x+ − + = +   ->(7 '3 7 ''0

++ x x

  − += =  

$ %&i ': -/  t ( ) ( )'0 * '1u x v x x= + = − +  c( * *7 7 '3uv u v= + −   * 7* 7

v uv u

= −⇔= +

.

3= ( )*

* '* ' 4 *

7

 x x x

−+ + − =   ->(

' 40

* * x x= − =  

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7/25/2019 Tai Lieu 6

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8= 7 778 * 4+ * 7 x x− + + =   ->( '80 *4 x x= − =  

9= ( ) ( ) ( )* 4 7 4 *7 7 7' ' ' ' x x x x x x x x+ − + − = − + + −   ->(

'10 0 '

* x x x= = =  

???@hAc c<c B; thCnh cng???

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