Complete the paragraph proof.
Given: M is the midpoint of PK
PK ⊥ MB
Prove: △PKB is isosceles
It is given that M is the midpoint of PK and PK ⊥ MB. Midpoints divide a segment into two congruent segments, so PM ≅ KM. Since PK ⊥ MB and perpendicular lines intersect at right angles, ∠PMB and ∠KMB are right angles. Right angles are congruent, so ∠PMB ≅ ∠KMB. The triangles share MB, and the reflexive property justifies that MB ≅ MB. Therefore, △PMB ≅ △KMB by the SAS congruence theorem. Thus, BP ≅ BK because
(corresponding parts of congruent triangles are congruent)
(base angles of isosceles triangles are congruent)
(of the definition of congruent segments)
(of the definition of isosceles triangles)
Finally, △PKB is isosceles because it has two congruent sides.