Observe the figure clearly.
To Prove: KA = KC
Proof:
Consider the triangles [tex]\Delta KAB , \Delta KCB[/tex]
KB = KB (Common side)
[tex]\angle KAB = \angle KCB[/tex] (each angle is of 90 degree)
[tex]\angle ABK = \angle KBC[/tex] (As BY bisects angle ABC)
Therefore, [tex]\Delta KAB \cong \Delta KCB[/tex]
By AAS congruence Theorem which states:
"If two angles and a non-included side of one triangle are congruent to the corresponding parts of another triangle, then the triangles are congruent".
Hence, the given triangles are congruent by AAS congruence criteria.