[DS12.C4.2.D03.c] Cho số phức
thỏa
. Mệnh đề nào dưới đây đúng?
A.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562373598_images/obj20203509928443215562373598_img1.png)
B.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562212697_images/obj20203509928443215562212697_img1.png)
C.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562448248_images/obj20203509928443215562448248_img1.png)
D.
.
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562857297_images/obj20203509928443215562857297_img1.png)
Đáp án và lời giải
Đáp án:B
Lời giải:
Ta có:
Đặt
, khi đó:
![img1](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562219492_images/obj20203509928443215562219492_img1.png)
![img2](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562219492_images/obj20203509928443215562219492_img2.png)
![img3](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562219492_images/obj20203509928443215562219492_img3.png)
![img4](https://cungthi.online/upload/questionbank3_20201220/eduquestion/20203509928443215562/obj20203509928443215562219492_images/obj20203509928443215562219492_img4.png)