题目内容
求值:
(1)若a=
+1,b=
-1,求a2b+ab2的值;
(2)若x+y=-5,xy=3,求
+
的值.
(1)若a=
3 |
3 |
(2)若x+y=-5,xy=3,求
|
|
(1)∵a=
+1,b=
-1,
∴a+b=2
,ab=(
)2-1=2,
∴a2b+ab2=ab(a+b)=2×2
=4
;
(2)∵x+y=-5,xy=3,
∴x<0,y<0,
∴
+
=
+
=
+
=-
-
=-
•
=-
×
=
.
3 |
3 |
∴a+b=2
3 |
3 |
∴a2b+ab2=ab(a+b)=2×2
3 |
3 |
(2)∵x+y=-5,xy=3,
∴x<0,y<0,
∴
|
|
|
|
=
| ||
|x| |
| ||
|y| |
=-
| ||
x |
| ||
y |
=-
xy |
x+y |
xy |
=-
3 |
-5 |
3 |
=
5
| ||
3 |
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