bai 7 phep nhan cac phan thuc dai so

Bµi 7: PhÐp nh©n c¸c ph©n thøc sè
1. Quy t¾c: Muèn nh©n hai
ph©n thøc, ta nh©n c¸c tö thøc
víi nhau, c¸c mÉu thøc víi nhau.

DB
CA
D
C
B
A
.
.
. =
? 1 Thùc hiÖn phÐp nh©n hai
ph©n thøc sau
3
22
6
25
.
5
3
x
x
x
x −
+
( )
( )

32
22
6.5
25.3
xx
xx
−
−
=
( )( )
( )
xxx
xxx
.3.5
55.3
2
2
+
−+
=
x
x
2
5−
=

VÝ dô :Thùc hiÖn phÐp nh©nph©n thøc
VÝ dô :Thùc hiÖn phÐp nh©nph©n thøc

( )
=+⋅
++
63
882
2
2
x
xx
x
( )
=
++
+⋅
=
+
⋅
++
=
882
63
1
63
882
2
2
2
2
xx
xxx

xx
x
( )
( )
( )
( )
( )
22
3
22
23
442
23
2
2
2
2
2
+
=
+
+
=
++
+
=
x
x
x
xx

xx
xx
B­íc 1: Nh©n hai ph©n thøc ( tö nh©n tö vµ mÉu nh©n mÉu)
B­íc 2: Ph©n tÝch rót gän ph©n thøc (nÕu cã)

Bµi tËp: thùc hiÖn c¸c phÐp tÝnh sau.
=⋅
2
2
3
7
214
,
x
y
y
x
a
( )
( )
=
+
−
⋅
−
++
3
3
2
32

1
1
96
,
x
x
x
xx
c
( )
=








−
−⋅
−
13
3
2
13
,
2
5
2

x
x
x
x
b
=
23
2
7.
2.14
xy
yx
( )
( )
( )
13.2
3.13
13
3
2
13
5
2
2
2
5
2
−
−
−=

−
⋅
−
−=
xx
xx
x
x
x
x
( )
( )
3
3
2
133
2
3.13
x
x
x
x
−
=
−
−=
( )
( )
( )
( )

3
32
32
1
1
3
+
−
⋅
−
+
=
x
x
x
x
( ) ( )
( ) ( )
( )
( )
32
1
32.1
1.3
2
3
32
+
−−
=

+−−
−+
=
x
x
xx
xx
=
xy.
4
xy
4

2. TÝnh chÊt
=⋅
D
C
B
A
B
A
D
C
a. Giao ho¸n
. .
b. KÕt hîp
B
A
D
C

F
E
B
A
D
C
F
E
.
.
.
.
=
F
E
B
A
D
C
B
A
F
E
D
C
B
A
⋅+⋅=







+
c, Ph©n phèi ®èi víi phÐp céng

?4 TÝnh nhanh :
153
27
3227
153
35
24
24
35
++
+−
⋅
+
⋅
+−
++
xx
xx
x
x
xx
xx
153

27
35
24
++
+−
⋅
xx
xx
27
153
24
35
+−
++
=
xx
xx
=
++
+−
⋅
+
⋅
+−
++
153
27
3227
153
35

24
24
35
xx
xx
x
x
xx
xx
32 +
⋅
x
x
3232
1
+
=
+
⋅=
x
x
x
x
Gi¶i