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Cho z1,z2z1,z2 là các số phức thỏa mãn $\Large \left

4.7/5

Tác giả: Thầy Tùng

Đăng ngày: 18 Aug 2022

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Câu hỏi:

Cho z1,z2z1,z2 là các số phức thỏa mãn |z1|=|z2|=1|z1|=|z2|=1|z12z2|=6|z12z2|=6. Tính giá trị của biểu thức P=|2z1+z2|P=|2z1+z2|.

Đáp án án đúng là: A

Lời giải chi tiết:

CÁCH 1:

Chọn z1=1z1=1.

Ta có hệ phương trình:

{|z2|=1|12z2|=6{x2+y2=1(12x)2+4y2=6{x2+y2=14x2+4y24x=5{x=14y=±154

TH1: z2=14+154i

P=|2.114+154i|=72+154=2

TH2: z2=14154i

P=|2.114154i|=72+154=2

CÁCH 2:

|z12z2|=6|z12z2|2=6|z1|2+4|z2|24|z1||z2|.cos(z1,z2)=6

cos(z1,z2)=14

P2=|2z1+z2|2=4|z1|2+|z2|2+4|z1||z2|.cos(z1,z2)=4+1+4(14)=4

Vậy P=2.