Line up the straight edge of the protractor with one side of the triangle. The ends of the protractor can extend beyond the triangle.
Slide the protractor along the line until the 90-degree mark lies on the opposite angle. Mark the point on the triangle side that lies directly under the center point of the protractor.
Place the straight edge so that it joins the point on the side with the tip of the opposite angle.
Draw a line. The line bisects the angle and lies perpendicular, or at a 90-degree angle from the side. This is the altitude of the angle.
Repeat Steps 1 through 4 on the other two angles and sides.