Cho hệ phương trình

B

- Hướng dẫn giải

Đáp án B

Ta có

$$\begin{gathered} \left\{\begin{array}{l}x-y=5\\ 3x+2y=18\end{array}\right.\iff \left\{\begin{array}{l}x=y+5\\ 3.\left(y+5\right)+2y=18\end{array}\right. \\ \iff \left\{\begin{array}{l}x=y+5\\ 3y+15+2y=18\end{array}\right.\iff \left\{\begin{array}{l}x=y+5\\ 5y=3\end{array}\right. \\ \iff \left\{\begin{array}{l}y=\frac{3}{5}\\ x=5+\frac{3}{5}\end{array}\right.\iff \left\{\begin{array}{l}x=\frac{28}{5}\\ y=\frac{3}{5}\end{array}\right. \end{gathered}$$

Vậy hệ phương trình có nghiệm duy nhất $\left(x{}_0;{\text{y}}_0\right)=\left(\frac{28}{5};\frac{3}{5}\right)\Rightarrow x_0.{\text{y}}_0\text{=}\frac{84}{25}$