[tex]\begin{cases} 8x-y=-3\\ x+4y=-21 \end{cases}\\\\\begin{cases} y=8x+3\\ x+4y=-21 \end{cases}\\\\ \begin{cases} y=8x+3\\ x+4 (8x+3)=-21 \end{cases}\\\\ \begin{cases} y=8x+3\\ x+32x+12=-21 \end{cases}\\\\ \begin{cases} y=8x+3\\ 33x =-21-12 \end{cases}\\\\[/tex]
[tex]\begin{cases} y=8x+3\\ 33x =-33\ \ |:33 \end{cases}\\\\ \begin{cases} y=8x+3\\ x =-1 \end{cases}\\\\ \begin{cases} y=8*(-1)+3\\ x =-1\end{cases}\\\\ \begin{cases} y=-5\\ x =-1 \end{cases}\\\\[/tex]
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[tex]\begin{cases} x+5y=-24\\3x+y=5\end{cases} \\\\ \begin{cases} x=-5y -24\\3 (-5y-24)+y=5\end{cases} \\\\ \begin{cases} x=-5y -24\\-15y-72+y=5\end{cases} \\\\ \begin{cases} x=-5y -24\\-14y =5+72\end{cases} \\\\\begin{cases} x=-5y -24\\-14y =77\ \ :(-14)\end{cases} \\\\ \begin{cases} x=-5y -24\\ y = -\frac{77}{7}\end{cases} \\\\[/tex]
[tex]\begin{cases} x=-5 *(-\frac{11}{2}) -24\\ y = -\frac{11}{2}\end{cases} \\\\ \begin{cases} x= \frac{55}{2} -24\\ y = -\frac{11}{2}\end{cases} \\\\ \begin{cases} x= \frac{55}{2} - \frac{48}{2}\\ y = -\frac{11}{2}\end{cases} \\\\ \begin{cases} x= \frac{7}{2} \\ y = -\frac{11}{2}\end{cases}[/tex]
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[tex]\begin{cases}4x-3y=11\ \ |*(-3)\\2x-9y=43 \end{cases}\\\\\begin{cases}-12x+9y=-33\\2x-9y=43 \end{cases}\\+------\\-10x=10\ \ |:(-10)\\x=-1\\\\4x-3y=11\\4*(-1)-3y=11\\-4-3y=11\\-3y=11+4\\-3y=15\ \ |:(-3)\\y=-5\\\\\begin{cases}x=-1\\y=-5 \end{cases}[/tex]
