Plot the points and draw the triangle. Now you have to draw a line that passes through a point, perpendicular to the triangle side that it's opposite from. Then do that again with a second point. The intersection of these two points will give you the Orthocenter. (You don't need to do it for the third point; it will pass through it anyway, but you only need two intersecting lines to define a point!) Since AB is a horizontal line, it will probably be easiest to start with the line perpendicular to AB that passes through C. You'll find that this is just the vertical line x=1. Now just pick another point and do it again. (Hint: if you know two points, you can find their slope, and you know that lines perpendicular to each other have negative reciprocal slopes.)
