Answer:
y=-4x
Explanation:
You can graph it.. It might be easier for you to count than to use the formula for slope. We are counting from (0,0) to (2,-8)... I'm doing rise/run... I have to go down from (0,0) 8 units so the rise is -8 and the run is 2. So the slope is -8/2=-4.
We know the y-intercept is (0,0)... so the equation is y=-4x+0 or just y=-4x
Maybe you seen that this was proportional because it was a straight diagonal line going through the origin which we knew then that the line was already in the form of y=kx
Then you can look at the point (2,-8) and see what you need to do 2 to get -8 multiplication-wise.
2(-4)=-8
so
x(-4)=y
or
y=-4x