TiÕt 26:

quy ®ång mÉu
thøc

1/ T×m mÉu thøc
vÝ dô
chung1
5
,

4 x − 8x + 4 6 x − 6 x
2

2

4 x − 8 x + 4 = 4( x − 1)
2

6 x − 6 x = 6 x( x − 1)
2

MTC:

12 x( x − 1)

2

2


Quy ®ång mÉu thøc hai ph©n thc
5
sau:1
,
4x2 − 8x + 4 6 x2 − 6 x

Bµi
2
2
2
Ta
cã:4 x − 8 x + 4 = 4( x − 1) MTC: 12 x ( x − 1)
lµm
6 x 2 − 6 x = 6 x( x − 1)
NTP(1) lµ: 3x
NTP(2) lµ : 2(x-1)
1
1.3 x
3x
VËy:
=
=
4 x 2 − 8 x + 4 12 x( x − 1) 2 12 x( x − 1) 2
5
5.2( x − 1)
10( x − 1)
=
=
2
2

Nhãm
2
Nhãm
3
Nhãm

3x
x+3
b/
, 2
2x + 4 x − 4
x+5
x
c/ 2
,
x + 4 x + 4 3x + 6
1
8
d/
,
x + 2 2x − x2


2 x + 6 = 2( x + 3)
x 2 − 9 = ( x − 3)( x + 3)
MTC : 2( x − 3)( x + 3)
5
5
5( x − 3)
=


x 2 + 4 x + 4 = ( x + 2) 2
3 x + 6 = 3( x + 2)
MTC : 3( x + 2) 2
x
x
x( x + 2)
=
=
3 x + 6 3( x + 2) 3( x + 2) 2
x+5
x+5
3.( x + 5)
=
=
2
2
x + 4 x + 4 ( x + 2)
3( x + 2) 2


x+2
2 x − x 2 = x(2 − x)
MTC : x ( 2 − x )( x + 2)
1
x(2 − x)
=
x+2
x ( x + 2)(2 − x )
8