3 |
2 |
(2)设抛物线的解析式为:y=ax(x-3),
当x=
3 |
2 |
9 |
4 |
3 |
2 |
9 |
4 |
当x=
9 |
2 |
27 |
4 |
9 |
2 |
27 |
4 |
依题意得:
27 |
4 |
9 |
4 |
解得:a=
1 |
2 |
∴抛物线的解析式为:y=
1 |
2 |
3 |
2 |
(3)证明:过点E作ED⊥FG,垂足为D,
设E(x,
1 |
2 |
3 |
2 |
则F(x+3,
1 |
2 |
3 |
2 |
得:S梯形EFGH=
3 |
2 |
3 |
2 |
1 |
2 |
3 |
2 |
1 |
2 |
3 |
2 |
3 |
2 |
∵
1 |
6 |
1 |
6 |
3 |
2 |
∴S梯形EFGH=
1 |
6 |
1 |
6 |
3 |
2 |
3 |
2 |
9 |
4 |
3 |
2 |
9 |
4 |
9 |
2 |
27 |
4 |
9 |
2 |
27 |
4 |
27 |
4 |
9 |
4 |
1 |
2 |
1 |
2 |
3 |
2 |
1 |
2 |
3 |
2 |
1 |
2 |
3 |
2 |
3 |
2 |
3 |
2 |
1 |
2 |
3 |
2 |
1 |
2 |
3 |
2 |
3 |
2 |
1 |
6 |
1 |
6 |
3 |
2 |
1 |
6 |