Question

giải/hệ/pt

x+y=80

2x+3y=198

Answer 1

\(\left\{{}\begin{matrix}x+y=80\\2x+3y=198\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}3x+3y=240\\2x+3y=198\end{matrix}\right.\)

\(\left\{{}\begin{matrix}x+y=80\\x=240-198=42\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=42\\y=38\end{matrix}\right.\)

 

Answer 2

\(\left\{{}\begin{matrix}x+y=80\\2x+3y=198\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}2x+2y=160\\2x+3y=198\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}y=38\\2x+3\cdot38=198\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}y=38\\2x=84\end{matrix}\right.\)

⇔\(\left\{{}\begin{matrix}y=38\\x=42\end{matrix}\right.\)

Vậy (42;38) là nghiệm