which type of triangle must have perpendicular lines
Perpendicular The legs of a right triangle are perpendicular to each other.
Right triangle The side opposite the right angle is called the hypotenuse (side c in the figure). The sides adjacent to the right angle are called legs (or catheti, singular: cathetus). Side a may be identified as the side adjacent to angle B and opposed to (or opposite) angle A, while side b is the side adjacent to angle A and opposed to angle B.