Question 768617
{{{x+y=-1}}}
{{{x-y=17}}}
________________add both

{{{x+y+x-y=-1+17}}}

{{{2x+cross(y)-cross(y)=16}}}

{{{2x=16}}}

{{{x=16/2}}}

{{{x=8}}}

now find {{{y}}}

{{{x+y=-1}}}

{{{8+y=-1}}}

{{{y=-1-8}}}

{{{y=-9}}}