Question 949229
{{{-y=2x}}}.....write in standard form
{{{3x+y=20}}}
-----------------

{{{-2x-y=0}}}...both sides multiply by {{{3}}}
{{{3x+y=20}}}...both sides multiply by {{{2}}}
-----------------

{{{-6x-3y=0}}}
{{{6x+2y=40}}}
-----------------...add

{{{-6x-3y+6x+2y=0+40}}}

{{{-3y+2y=40}}}

{{{-y=40}}}

{{{y=40/-1}}}

{{{y=-40}}}

now find {{{x}}}

{{{-y=2x}}}

{{{-(-40)=2x}}}

{{{40=2x}}}

{{{40/2=x}}}

{{{x=20}}}

so, the system has one solution

these lines intersect at ({{{20}}},{{{-40}}})

{{{ graph( 600, 600, -55, 55, -55, 55, -2x,-3x+20) }}}