Question 820750
equation 1{{{x=y-8 }}}
equation 2{{{-x-y=0}}}

Substitute eq 1 to eq 2

{{{ -x-y=0}}} x=y-8
{{{ -(y-8)-y=0 }}}
{{{ -y+8-y=0}}}
{{{ -2y=-8}}}
{{{ -2y/-2=-8/-2}}}
{{{ highlight (y=4) }}}
{{{ x=y-8}}} y=4
{{{ x=4-8}}}
{{{ highlight (x=-4)}}}