Answer:
y = -2x
Explanation
slope intercept form: y = mx + b
m is slope and b is y-intercept
1. lets find y-intercept cuz thats easiest
the line crosses (0,0) at the y-axis so there is no y-intercept
2. to find slope rise/run
we'll start at (0,0) since that's the y-intercept
3. slope is rise/run = -2/1 = -2
it's negative becuase it's going left
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another way you can find slope is by the equation y2 - y1/ x2 - x1
take 2 random points from the line, i will use (0,0) and (-2,4)
4 - 0/ -2 - 0 = 4/-2 = -2
slope is -2