To do that, you need to set it all to zero and factor: x^2+8x+15 = 0 (x+5)(x+3) = 0 then put both those in parentheses chunks in their own equations x + 5 = 0 x + 3 = 0 and then simplify x = -5 x = -3 So the two points where the parabola crosses the x-axis are -5 and -3.