Use the Show Object and Hide Object features to compare the various functions to f(x). Decide which ones are parallel to f(x) and make a conjecture on why they are parallel lines.
Now, use the Show and Hide Object Features to find which function is perpendicular to f(x). Come up with a conjecture on why these two functions are perpendicular.
Now, test this conjecture to find the last pair of functions that are also perpendicular!
(They are not necessarily perpendicular to f(x).)

To test if the functions are actually perpendicular to each other plot a point somewhere on each line and at their intersection. Then go to the Angle icon, click it, then highlight the points from right to left around the angle of interest. It should show you the measure of the angle and tell you if it is 90 degrees or not.