Question

Tìm x, y, z biết :

x + y +z = 73

xy = 5z + 2

x + z = 2y

Answer 1

#They're all bad roots.

_Solution

Ta có: \(\left\{{}\begin{matrix}x+y+z=73\left(1\right)\\xy=5z+2\left(2\right)\\x+z=2y\left(3\right)\end{matrix}\right.\)

Thay (3) vào (1) \(\Rightarrow3y=73\Rightarrow y=\frac{73}{3}\) (*)

Thay (*) vào (2) \(\Leftrightarrow\frac{73x}{3}=5z+2\Leftrightarrow z=\frac{73x-6}{15}\) (**)

Thay (**) vào (2) \(\Leftrightarrow x+\frac{73x-6}{15}=\frac{2.73}{3}\)

\(\Leftrightarrow\frac{88x-6}{15}=\frac{146}{3}\Leftrightarrow x=\frac{92}{11}\) \(\Rightarrow\) Thay vào (3) \(\Rightarrow z=\frac{1330}{33}\)