Cho tam giác
trên cạnh
lấy điểm
sao cho
. Trên cạnh
lấy điểm
sao cho
. Gọi
là trung điểm của
. Tia
cắt
tại
. Tỉ số
có giá trị là
A.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161666236_images/obj20205919623623384161666236_img1.png)
B.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161601316_images/obj20205919623623384161601316_img1.png)
C.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161168000_images/obj20205919623623384161168000_img1.png)
D.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161867930_images/obj20205919623623384161867930_img1.png)
Đáp án và lời giải
Đáp án:B
Lời giải:
Đặt
.
Ta có
Mặt khác
.
Từ và , để
thẳng hàng ta có
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161304705_images/obj20205919623623384161304705_img1.png)
![img2](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161304705_images/obj20205919623623384161304705_img2.png)
![img3](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161304705_images/obj20205919623623384161304705_img3.png)
![img4](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161304705_images/obj20205919623623384161304705_img4.png)
![img5](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161304705_images/obj20205919623623384161304705_img5.png)
![img6](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20205919623623384161/obj20205919623623384161304705_images/obj20205919623623384161304705_img6.png)