It is given that m is the midpoint of and. Midpoints divide a segment into two congruent segments, so. Since and perpendicular lines intersect at right angles, and are right angles. Right angles are congruent, so. The triangles share , and the reflexive property justifies that. Therefore, by the sas congruence theorem. Thus, because . Finally, δpkb is isosceles because it has two congruent sides. Corresponding parts of congruent triangles are congruent base angles of isosceles triangles are congruent of the definition of congruent segments of the definition of a right triangle.