Trong mặt phẳng tọa độ
, tọa độ điểm
trên cạnh
của tam giác
có
,
,
sao cho
là
![img1](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img1.png)
![img2](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img2.png)
![img3](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img3.png)
![img4](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img4.png)
![img5](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img5.png)
![img6](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img6.png)
![img7](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img7.png)
![img8](https://cungthi.online/upload/questionbank3/eduquestion/20180821605413142752/obj20180821605413142752420967_images/obj20180821605413142752420967_img8.png)
A.
B.
C.
D.
Đáp án và lời giải
Đáp án:B
Lời giải:
Phân tích: Gọi là chân đường cao kẻ từ
của tam giác
. Theo đề ta có:
. Ta có
;
. Do đó
. Vậy
.
Đáp án đúng là B