Question 995318

{{{x+y=9}}}...eq.1 
{{{4x+y=9}}}...eq.2
----------------------subtract eq.1 from eq.2

{{{4x+y-(x+y)=9-9}}}
{{{4x+cross(y)-x-cross(y)=0}}}
{{{3x=0}}}
{{{highlight(x=0)}}}

go to eq.1, plug in {{{0}}} for {{{x}}}

{{{x+y=9}}}...eq.1 
{{{0+y=9}}}
{{{highlight(y=9)}}}

so, these two lines intersecting each other in one point, ({{{0}}},{{{9}}})


{{{ graph( 600, 600, -10, 10, -10, 10, -x+9,-4x+9) }}}