Answer:
90° + (γ/2)
Step-by-step explanation:
The angles in ΔADB have a sum of 180°, so ...
(A/2) +(B/2) + ∠ADB = 180°
and so do the angles of ΔABC:
A + B + γ = 180°
Dividing this second equation by 2 gives an expression for (A/2) +(B/2) that we can substitute into the first equation:
A/2 +B/2 +γ/2 = 90°
A/2 +B/2 = 90° -γ/2
Putting this in the first equation, we have ...
(90° -γ/2) + ∠ADB = 180°
∠ADB = 90° +γ/2 . . . . . . . . . . add (γ/2 -90°)
