What is an equation for this line?

Answer:
The equation of the line is y=-x
Step-by-step explanation:
To find the equation for a line, we need to know 2 points.
One of the points is (0,0) because it goes through the origin. Another point is (5,-5). We can calculate the slope because we have 2 points using the formula.
m = (y2-y1)/(m2-m1)
m = (-5-0)/(5-0)
m = -5/5
m=-1
The slope is -1
We know the y intercept (where it crosses the y axis) is 0. Using the slope intercept form of a line
y = mx+b
y =-1x+ 0
y = -x
The equation of the line is y=-x