Question

What's substitution for: X=y-7 X+8y=2

Answer 1

$\left \{ {{x=y-7} \atop {x+8y=2}} \right. \\\\ substitute\ x=y-7\ into \ the\ second\ equation\\\\ y-7+8y=2\\\\ 9y-7=2\ \ \ | add\ 7\\\\ 9y=9\ \ \ | divide\ by\ 9\\\\ y=1\\\\x=y-7=1-7=-6$