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§¹i sè
§¹i sè
§¹i sè
§¹i sè
Líp 7

-
Häc sinh 1: S¾p xÕp Q(x) theo luü thõa gi¶m
dÇn cña biÕn
Q(x) = x
2
+ 2x
4
+ 4x
3
+ 3x
2
- 4x -1
KiÓm tra bµi cò
- Häc sinh 2 + C¶ líp:
Q(x) = 2x
5
+5x
4
- x
3
+ x
2
- x - 1
P(x) = -x

4
+ x
3
+ 5x+ 2
TÝnh P(x) + Q(x)

1. Q(x) = 2x
4
+ 4x
3
+ (3x
2
+ x
2
) - 4x -1
= 2x
4
+ 4x
3
+ 4x
2
- 4x -1
KiÓm tra bµi cò
2. Q(x) = 2x
5
+5x
4
- x
3
+ x

2
– x – 1
P(x) = -x
4
+ x
3
+ 5x+ 2
* P(x) + Q(x)
= 2x
5
+5x
-
- x
3
+ x
2
- x - 1 -x
4
+ x
3
+ 5x+ 2
= 2x
5
+ (5x
4
- x
4
) +

(- x

3
+ x
3
) + x
2
+(5x - x)+(2 - 1)
= 2x
5
+ 4x
4
+

x
2
+ 4x + 1

TiÕt 60 : Céng, trõ ®a thøc
mét biÕn
1. Céng hai ®a thøc mét biÕn
a. VÝ dô
Q(x) = 2x
5
+5x
4
- x
3
+ x
2
– x – 1
P(x) = -x

4
+ x
3
+ 5x + 2
TÝnh P(x) + Q(x)
C¸ch 1:
P(x) +Q(x) = 2x
5
+5x
4
- x
3
+ x
2
- x - 1 -x
4
+ x
3
+ 5x+ 2
= 2x
5
+ (5x
4
- x
4
) +

(-x
3
+ x

3
) + x
2
+(5x - x)+(2 - 1)
= 2x
5
+ 4x
4
+

x
2
+ 4x + 1
C¸ch 2: Céng 2 ®a thøc theo cét däc
P(x) = 2x
5
+5x
4
- x
3
+ x
2
- x - 1
Q(x) = -x
4
+ x
3
+ 5x + 2
P(x) +Q(x) = 2x
5

+ 4x
4
+

x
2
+ 4x + 1

Muèn céng 2 ®a thøc mét
biÕn ta lµm nh­ thÕ nµo?

TiÕt 60 : Céng, trõ ®a thøc
mét biÕn
1. Céng hai ®a thøc mét biÕn
a. VÝ dô
Q(x) = 2x
5
+ 5x
4
- x
3
+ x
2
- x - 1
P(x) = - x
4
+ x
3
+ 5x + 2
TÝnh P(x) + Q(x)

b. KÕt luËn
§Ó céng hai ®a thøc mét biÕn, ta cã thÓ thùc hiÖn mét trong hai
c¸ch sau
C¸ch 1: Thùc hiÖn theo céng ®a thøc
C¸ch 2: Céng hai ®a thøc theo cét däc

Bµi 44 – SGK 45
P(x) = - 5x
3
- + 8x
4
+ x
2
Q(x) = x
2
– 5x- 2x
3
+ x
4
-
TÝnh P(x) + Q(x)
(D·y ph¶i céng theo c¸ch 1- D·y tr¸i céng theo c¸ch 2)
C¸ch 2:
P(x) = 8x
4
- 5x
3
+ x
2
-

Q(x) = x
4
- 2x
3
+ x
2
- 5x -
P(x) + Q(x) = 9x
4
– 7x
3
+2x
2
– 5x + 1
C¸ch 1:
P(x) +Q(x) = - 5x
3
- + 8x
4
+ x
2
+ x
2
– 5x- 2x
3
+ x
4
-
= (8x
4

+x
4
)+(-5x
3
-2x
3
)+(x
2
+ x
2
)+( + )
= 9x
4
– 7x
3
+2x
2
– 5x + 1
3
1
3
2
3
1
3
1
3
2
3
2

3
1
3
2