Help me please.

y=2x
x+y=0

im working on solving systems by graphing. I don't know how slope work yet, right now we working on x and y intercepts. I'm Lose please help

use 2 x for y

x + 2x = 0
3 x = 0
x = 0
y = 0
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to graph
first one
when x = 0, y = 0, so through origin (0,0)
pick another x
when x = 1, y = 2 so through (1,2)
draw that line
second one
when x = 0, y = 0, so through origin (0,0)
when x = 1, y = -1, so through (1,-1)
draw that line.
They cross, sure enough, at (0,0)