Can a triangle have perpendicular sides?

A triangle can have one angle made up of perpendicular lines. That would be called a right triangle. A triangle cannot have more than one angle made up of perpendicular lines however. To see why, remember that an angle created by two perpendicular lines is 90 degrees and a triangle is made up of three angles that sum to 180 degrees. If two angles were 90 degrees the third angle would have to be 0 degrees, in which case the shape is no longer a triangle.