Cho hình chóp tứ giác đều
có cạnh đáy bằng
. Gọi
là điểm trên cạnh
sao cho
. Góc giữa
và mặt phẳng đáy một góc
. Tính thể tích
của khối chóp
.
A.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323636408_images/obj20174028494217405323636408_img1.png)
B.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323651939_images/obj20174028494217405323651939_img1.png)
C.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323522030_images/obj20174028494217405323522030_img1.png)
D.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323218624_images/obj20174028494217405323218624_img1.png)
Đáp án và lời giải
Đáp án:A
Lời giải:
Ta có
;
Áp dụng định lí cosin trong
vuông cân tại
nên
.
Vậy đáp án đúng là A.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img1.png)
![img2](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img2.png)
![img3](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img3.png)
![img4](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img4.png)
![img5](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img5.png)
![img6](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img6.png)
![img7](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img7.png)
![img8](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img8.png)
![img9](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img9.png)
![img10](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img10.png)
![img11](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img11.png)
![img12](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img12.png)
![img13](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20174028494217405323/obj20174028494217405323946610_images/obj20174028494217405323946610_img13.png)