Find the equation of the normal line to the graph of the function

f(x) = sec^2(pi x) at the point with x-coordinate 1/4.

Where does f(x) have horizontal tangent lines?

Ok, so I pluged in 1/4 for x and solved for y and got 2. Then how do I do the equation of the line? I don't know how to get the slope for the equation. The answer is in point-slope form.