The quadratic function has two roots; one at x = 1 and one at x = 9. We make a function y = (x-1)(x-9), but would open up instead of down. So, we multiply it by -1, and get y = -(x-1)(x-9). We read from the graph that the points of intersection of the two graphs are x = 2 and x = 6. Plugging these into the formula for y get y = 7 and y = 15, respectively. The slope between (2,7) and (6,15) is 2. The point-slope formula then gives us y - 15 = 2(x-6).