What is the equation of a line with endpoints (0,0) and (2,-8)

y=-4x

Step-by-step 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