!"#
=
=
=
⇒
=
=
=
!"#$
% &#!
#'()*+%
,# /0# 1#
⇒
$%&'()&*+,!-
(23#)456
=
=
b, TÝnh M N –
a, M + N = (x
2
– 2xy + y
2
) + (y
2
+ 2xy + x
2
+ 1)
= x
2
– 2xy + y
2
+ y
2
+ 2xy + x
2
+ 1
= (x
2
+ x
2
) + ( -2xy + 2xy) + (y
2
+ y
2
) + 1
= 2x
2
+ 2y
2
+ 1
a, M - N = (x
2
– 2xy + y
2
) - (y
2
+ 2xy + x
2
+ 1)
= x
2
– 2xy + y
2
- y
2
- 2xy - x
2
- 1
= (x
2
- x
2
) + ( -2xy - 2xy) + (y
2
- y
2
) - 1 = - 4xy - 1
./01234
$%&'()&*+,!-
(73#)4589
9
:
;<=98 >89
= x
2
2y + xy + 1 + x–
2
+ y x–
2
y
2
1–
= (x
2
+ x
2
) + (-2y + y) + (1 - 1) + xy x–
2
y
2
= 2x
2
- y + xy x–
2
y
2
VËy: C = 2x
2
y + xy x– –
2
y
2
= x
2
+ y - x
2
y
2
- 1 - x
2
+ 2y - xy - 1
= (x
2
- x
2
) + (y + 2y) + (-1 - 1) - xy - x
2
y
2
= 3y - 2 - xy - x
2
y
2
VËy C = 3y - 2 - xy - x
2
y
2
Gi¶i
a, V× C = A + B
Ta cã A + B = (x
2
2y + xy + 1) + (x–
2
+ y x–
2
y
2
- 1)
⇒b, Tõ C + A = B C = B - A
Ta cã: B - A = (x
2
+ y - x
2
y
2
- 1) - (x
2
- 2y + xy + 1)
./01234
$%&'()&*+,!-
$%&5(&67!,!-
(?%#-@A<B="
1==:
>
5
5
C
C
D
D
1=:=:
66D
66D
66D
66D
66D>*=6
==:'(E
FF::
=
:
E
=
=5:5:=:
G?#-@A1==:H(:
./01234
>=:=:'(E
:F::
F
:
:
5F
:
5
:
CF
:
C
:
D
:
D
$%&'()&*+,!-
$%&5(&67!,!-
(#-@A<B="
1==:
>
5
5
C
C
D
D
1=:=:
66D
66D
66D
66D
66D>*=6
==
G?#-@A1=:=:H(
./01234
E
66D
66D
66D
66D
+ 2008
9
66I
F
66D
F
66D
66I
+ 2008
$%&'()&*+,!-
$%&5(&67!,!-
(#-@A<B="
1==:
>
5
5
C
C
D
D
1=:=:
66D
66D
66D
66D
66D>*=6
9
66I
F
66D
F
66D
66I
+ 2008
V× x - y = 0 ta cã x
2008
.0 + y
2008
.0 + 2008 = 2008
./01234
9
66D
66D
66D
$%&'()&*+,!-
$%&5(&67!,!-
89:&;
:J<'K#>LM,# #
-@A<,>N"F
:O(<>(573P-#5
:QR<H1>(?%SH(<
./01234
./01234
⇒
Bµi 34 Sgk/ 40: TÝnh tæng c¸c ®a thøc:
a, P = x
2
y + xy
2
5x–
2
y
2
+ x
3
vµ Q = 3xy
2
x–
2
y + x
2
y
2
b, M = x
3
+ xy + y
2
x–
2
y
2
2 – vµ N = x
2
y
2
+ 5 y–
2
Gi¶i
a, P + Q = (x
2
y + xy
2
– 5x
2
y
2
+ x
3
) + ( 3xy
2
– x
2
y + x
2
y
2
)
= x
2
y
+ xy
2
– 5x
2
y
2
+ x
3
+ 3xy
2
– x
2
y + x
2
y
2
= (x
2
y – x
2
y ) + (xy
2
+ 3xy
2
) + (- 5x
2
y
2
+ x
2
y
2
) + x
3
= 4xy
2
– 4x
2
y
2
+ x
3
b, M + N = (x
3
+ xy + y
2
– x
2
y
2
- 2) + (x
2
y
2
+ 5 – y
2
)
= x
3
+ xy + y
2
– x
2
y
2
– 2 + x
2
y
2
+ 5 – y
2
= (y
2
– y
2
) + ( -x
2
y
2
+ x
2
y
2
) +( -2 + 5)+ x
3
+ xy
= 3 + x
3
+ xy
⇒
8=
=
:
=:
8:
=(
)(
)(
)
E8=
=
=
=(
)()(
)(:)
./01234