Question

1) {2x−y=12
{x−5,5y=9
2){y+9x=2
{4y−9x=4

Answer 1

$\displaystyle\bf\\\left \{ {{2x-y=12} \atop {x-5,5y=9}} \right. \\\\\\\left \{ {{y=2x-12} \atop {x-5,5\cdot(2x-12)=9}} \right. \\\\\\\left \{ {{y=2x-12} \atop {x-11x+66=9}} \right. \\\\\\\left \{ {{y=2x-12} \atop {-10x=9-66}} \right. \\\\\\\left \{ {{y=2x-12} \atop {-10x=-57}} \right. \\\\\\\left \{ {{y=2\cdot 5,7-12} \atop {x=5,7}} \right.\\\\\\\left \{ {{y=11,4-12} \atop {x=5,7}} \right. \\\\\\\left \{ {{y=-0,6} \atop {x=5,7}} \right. \\\\\\Otvet \ : \ (5,7 \ ; \ -0,6)$

$\displaystyle\bf\\2)\\\\+\left \{ {{y+9x=2} \atop {4y-9x=4}} \right. \\---------\\y+4y+9x-9x=2+4\\\\5y=6\\\\y=6:5=1,2\\\\9x=2-y=2-1,2=0,8\\\\x=0,8:9=\frac{8}{90} =\frac{4}{45} \\\\\\Otvet \ : \ \Big(\frac{4}{45} \ ; \ 1,2\Big)$