You can take the first point as the origin O(0,0) and the second one (-2,0.5) for easier calculations. Find the slope, m = (y2 - y1)/(x2 - x1) = -2-0 / -0.5-0 = 2/0.5 = 4
now take (x,y) = (0,0) and m= 4 use the point slope form (y - y1) = m(x - x1) (y - 0) = (4)(x - 0) ......taking (x1,y1) = (0,0) y = 4x + 0 ...... in the form of y = mx + b I hope I was helpful:)