Question 101653
First, pick x=0. 
{{{y=-2x}}}
{{{y(0)=-2(0)=0}}}
You now know the line goes through (0,0), the origin. 
Pick one more point x=1. 
{{{y=-2x}}}
{{{y(1)=-2(1)=-2}}} 
Another point is (1,-2). 
Two points is all you need to define a line. 
(0,0) and (1,-2)


{{{graph( 300, 200, -5, 5, -5, 5, -2x)}}}