khối chóp tam giác
có cạnh bên
vuông góc với mặt phẳng
, đáy là tam giác
cân tại
, độ dài trung tuyến
bằng
, cạnh bên
tạo với đáy góc
và tạo với mặt phẳng
góc
. Thể tích khối chóp
bằng
![img1](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img1.png)
![img2](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img2.png)
![img3](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img3.png)
![img4](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img4.png)
![img5](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img5.png)
![img6](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img6.png)
![img7](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img7.png)
![img8](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img8.png)
![img9](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img9.png)
![img10](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img10.png)
![img11](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img11.png)
![img12](https://cungthi.online/upload/questionbank3/eduquestion/2018372761266501598/obj2018372761266501598250585_images/obj2018372761266501598250585_img12.png)
A.
B.
C.
D.
Đáp án và lời giải
Đáp án:D
Lời giải:
Phân tích: Đặt . Ta có
. Ta có:
. Xét tam giác vuông SBD, ta có
. Khi đó:
. Vậy
.
Đáp án đúng là D