和上一张连着的卷子
来源:学生作业帮 编辑:搜狗做题网作业帮 分类:数学作业 时间:2024/07/07 10:03:33
和上一张连着的卷子
![](http://img.wesiedu.com/upload/2/15/215edb2fe24fbbc6066af5a04d1bf5a1.jpg)
![](http://img.wesiedu.com/upload/2/15/215edb2fe24fbbc6066af5a04d1bf5a1.jpg)
![和上一张连着的卷子](/uploads/image/z/17427805-61-5.jpg?t=%E5%92%8C%E4%B8%8A%E4%B8%80%E5%BC%A0%E8%BF%9E%E7%9D%80%E7%9A%84%E5%8D%B7%E5%AD%90+%26nbsp%3B)
![](http://img.wesiedu.com/upload/3/e5/3e5e4a204fef585f6480cdbeaca721fa.jpg)
16) y=x²/2-3x+4
=1/2(x²-6+8)
=1/2(x²-2·3+3²-1)
=1/2(x²-2·3+3²)-1/2
=1/2(x-3)²-1/2
所以其顶点为(3,-1/2)
对称轴 x=3
y=1/2(x-3)²-1/2<0
1/2(x-3)²<1/2
(x-3)²<1
-1<x-3<1
2<x<4
-----------------------------------------------------------------------------------------------
17)将(3,0)、(2,-3)代入y=x²+bx+c得:
0=3²+3b+c
-3=2²+2b+c
联立求解得:b=-2,c=-3
所以抛物线为y=x²-2x-3
其顶点P为[-b/(2a),(4ac-b²)/(4a)]
即P(1,-4)
与纵轴交点Q(0,-3)
OQ=0-(-3)=3
OQ边上的高为P到纵轴的距离1
所以S△OPQ=3×1÷2=1/2
![](http://img.wesiedu.com/upload/2/62/262ac5de2d71f3ba9c6e6f08ba66f052.jpg)