\(\hept{\begin{cases}6x-15y=10\\12x+21y=-8\end{cases}}\Leftrightarrow\hept{\begin{cases}12x-30y=20\\12x-21y=-8\end{cases}}\Leftrightarrow\hept{\begin{cases}x=\frac{5}{17}\\y=-\frac{28}{51}\end{cases}}\)
\(\hept{\begin{cases}2\left(3x-2\right)-4=5\left(3y+2\right)\\4\left(3x-2\right)+7\left(3y+2\right)=-2\end{cases}}\)
Đặt \(\hept{\begin{cases}3x-2=t\\3y+2=u\end{cases}}\)
Hệ trở thành : \(\hept{\begin{cases}2t-4=5u\\4t+7u=-2\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}2t-4-5u=0\\4t+7u-2=0\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}2\left(2t-4-5u\right)=0\\4t+7u+2=0\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}4t-8-10u=0\\4t+7u+2=0\end{cases}}\)
\(\Leftrightarrow4t-8-10u-4t-7u-2=0\)
\(\Leftrightarrow-10-17u=0\)
\(\Leftrightarrow-17u=10\)
\(\Leftrightarrow u=\frac{-10}{17}\)
\(\Leftrightarrow3y+2=\frac{-10}{17}\Rightarrow y=\frac{-44}{51}\)
Tìm ra t rùi thay vào tìm x nha
b/ đặt x-y =a, x+y=b trở về hpt ta đc \(\hept{\begin{cases}3b+5a=12\\-5b+2a=11\end{cases}}\Leftrightarrow\hept{\begin{cases}a=3\\b=-1\end{cases}}\Leftrightarrow\hept{\begin{cases}x-y=3\\x+y=-1\end{cases}}\Leftrightarrow\hept{\begin{cases}x=1\\y=-2\end{cases}}\)
