\(\hept{\begin{cases}2x+3y=4\\4x-2y=5\end{cases}}\)

<=> \(\hept{\begin{cases}4x+6y=8\\4x-2y=5\end{cases}}\)

<=>\(\hept{\begin{cases}8y=3\\2x+3y=4\end{cases}}\)

<=> \(\hept{\begin{cases}y=\frac{3}{8}\\2x+\frac{9}{8}=4\end{cases}}\)

<=> \(\hept{\begin{cases}y=\frac{3}{8}\\2x=\frac{23}{8}\end{cases}}\)

<=> \(\hept{\begin{cases}y=\frac{3}{8}\\x=\frac{23}{16}\end{cases}}\)

Vậy hệ phương trình có nghiệm (x;y) là \(\left(\frac{23}{16};\frac{3}{8}\right)\)

\(\left\{{}\begin{matrix}x^2+xy+y^2=1\\x-y-xy=3\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}\left(x-y\right)^2+3xy=1\\x-y-xy=3\end{matrix}\right.\)

Đặt \(\left\{{}\begin{matrix}x-y=u\\xy=v\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}u^2+3v=1\\u-v=3\end{matrix}\right.\)

\(\Rightarrow u^2+3\left(u-3\right)=1\)

\(\Leftrightarrow u^2+3u-10=0\Rightarrow\left[{}\begin{matrix}u=2\Rightarrow v=-1\\u=-5\Rightarrow v=-8\end{matrix}\right.\)

TH1: \(\left\{{}\begin{matrix}u=2\\v=-1\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x-y=2\\xy=-1\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}y=x-2\\xy=-1\end{matrix}\right.\)

\(\Rightarrow x\left(x-2\right)=-1\Leftrightarrow\left(x-1\right)^2=0\Rightarrow x=1\Rightarrow y=-1\)

TH2: \(\left\{{}\begin{matrix}u=-5\\v=-8\end{matrix}\right.\) \(\Rightarrow...\) bạn tự làm tương tự

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