The equation of a line is y = mx + b where m is the slope and b is the y-intercept (the point where the line crosses the y-axis). we can look at the graph and see that the line crosses the y axis at y = 4. Therefore, the y-intercept, b, is 4.
Now we must calculate the slope. To do so, we divide the "rise" of the line, y₂ - y₁ by the "run" of the line x₂ - x₁. We must choose two points (x₁, y₁) and (x₂, y₂) to find the slope. Two points are already given to us, (1, 2) and (4, -4):
m = (-4 - 2)/(4 - 1)
m = -6/3
m = -2
Now that we know the slope and the y-intercept, we can simply plug them back into the equation to find the equation of the line:
