题目内容
设方程4x2-7x-3=0的两个根为x1、x2,求下列各式的值:
(1)(x1-3)(x2-3);
(2)
+
.
(1)(x1-3)(x2-3);
(2)
x1 |
x2 |
x2 |
x1 |
根据题意得x1+x2=
,x1x2=-
,
(1)原式=x1x2-3(x1+x2)+9=-
-3×
+9=3;
(2)原式=
=
=
=-
.
7 |
4 |
3 |
4 |
(1)原式=x1x2-3(x1+x2)+9=-
3 |
4 |
7 |
4 |
(2)原式=
x12+x22 |
x1x2 |
(x1+x2)2-2x1x2 |
x1x2 |
(
| ||||
-
|
73 |
12 |
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