A

B

C

C, B

D

\(\left\{{}\begin{matrix}3x-y=5\\5x+2y=23\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}2.\left(3x-y\right)=2.5\\5x+2y=23\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}6x-2y=10\\5x+2y=23\end{matrix}\right.\)

<=>\(\left\{{}\begin{matrix}3x-y=5\\6x-2y+\left(5x+2y\right)=10+23\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}3x-y=5\\6x-2y+5x+2y=33\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}3x-y=5\\11x=33\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}3x-y=5\\x=3\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}3.3-y=5\\x=3\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}9-y=5\\x=3\end{matrix}\right.\)

<=> \(\left\{{}\begin{matrix}y=4\\x=3\end{matrix}\right.\)

Vậy nghiệm của hệ phương trình là\(\left\{{}\begin{matrix}x=3\\y=4\end{matrix}\right.\)

cái này bạn sử dụng hằng đẳng thức số 2 là được mà

2. is being affected by the pollution in the city.

3. have been awarded a prize for his essay.

4. wasn't writen by Peter.

5. candles made?

A