You can put this solution on YOUR website! , or a better form with which to work, . The line or lines tangent to the parabola will have slope .
Any general point on the parabola is (x, (x^2)/(4a)).
Pick any of these points you like as long as . Why? Because at x=0, the slope is 0, for a horizontal line, and will not make an angle with the x-axis. The question description specifies that the tangent line makes an angle with the x-axis.