Answer:
Step-by-step explanation:
If m∠ABC = 40° and BD is the bisector of ∠ABC, then
(1) m∠ABD = m∠DBC
(2) m∠ABC = m∠ABD + m∠DBC
From (1) and (2) we have:
m∠ABC = 2m∠ABD
Therefore
2m∠ABD = 40° divide both sides by 2
m∠ABD = 20°
