GỌI M(0; 0; Z)  ⃗⃗⃗⃗⃗⃗ ⃗⃗⃗⃗⃗⃗ GỌI D = MA2 + MB2 = 13 +...

Câu 11: Gọi M(0; 0; z)  ⃗⃗⃗⃗⃗⃗ ⃗⃗⃗⃗⃗⃗

Gọi d = MA

2

+ MB

2

= 13 + (2 – x)

2

+ 34 + (4 – x )

2

= 47 + (2 – x)

2

+ (4 – x)

2

Ta có : d’ = -2(2 – x) – 2(4 – x) = 0  x = 3  M (0; 0; 3)  D