Question

given that ba→ bisects ∠dbc, which statement must be true? m∠abd = m∠abc; b is the mid - point of dc¯; m∠dbc = 90°; ab¯≅bc¯

Explanation:

Step1: Analyze angle DBC

DB and BC are vertical opposite rays, so ∠DBC=180°.

Step2: BA bisects ∠DBC

Bisector BA splits 180° into two equal angles: ∠ABD=∠ABC=90°.

Step3: Evaluate options

∠ABD=∠ABC is true; others lack length/position info.

Answer:

m∠ABD = m∠ABC