Question

Giải hệ pt sau

 

X+y=25

5x+4y=120

Answer 1

\(\hept{\begin{cases}x+y=25\\5x+4y=120\end{cases}\Rightarrow\hept{\begin{cases}4x+4y=100\\5x+4y=120\end{cases}}}\)

\(\Rightarrow5x+4y-4x-4y=120-100\)

\(\Rightarrow x=20\)

\(\Rightarrow y=5\)

Answer 2

\(\hept{\begin{cases}x+y=25\\5x+4y=120\end{cases}\Leftrightarrow\hept{\begin{cases}x+y=25\\x+4\left(x+y\right)=120\end{cases}\Leftrightarrow}\hept{\begin{cases}x+y=25\\x+100=120\end{cases}\Leftrightarrow}\hept{\begin{cases}x=20\\y=5\end{cases}.}},\)

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