In △BAH and △CAK
AB = AC (Given congruent sides of triangle)
m∠BAK = m∠CAH ( Given congruent angles)
AH = AK (Given congruent sides of triangle)
Therefore, triangle △BAH congruent to triangle △CAK.
△BAH ≅ △CAK by (Side Angle Sngle or SAS triangle congruency postulate).
Therefore, m∠K = m∠H (Congurent parts of the congruent triangles are congruent).
