Question

Giải hệ phương trình bằng phương pháp cộng đại số

1)\(\left\{{}\begin{matrix}x+4y=2\\3x+2y=4\end{matrix}\right.\)

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

3)\(\left\{{}\begin{matrix}2x-3y=2\\-4x+6y=2\end{matrix}\right.\)

Answer 1

1) hpt \(\Leftrightarrow\left\{{}\begin{matrix}x+4y=2\\6x+4y=8\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}y=\dfrac{2-x}{4}\\5x=6\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}y=\dfrac{1}{5}\\x=\dfrac{6}{5}\end{matrix}\right.\)

Kl: x=6/5 và y=1/5

2) hpt \(\Leftrightarrow\left\{{}\begin{matrix}-2x-2y=4\\-2x-4y=0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=-2-y\\2y=4\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=-4\\y=2\end{matrix}\right.\)

Kl...

3) hpt \(\Leftrightarrow\left\{{}\begin{matrix}2x-3y=2\\2x-3y=-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{2+3y}{2}\\0=3\left(vô-lý\right)\end{matrix}\right.\)

kl: hpt vn