9514 1404 393
Answer:
48°
Step-by-step explanation:
The acute angles in a right triangle are complementary, so angle CAD is ...
∠CAD = 90° -60° = 30°
When an angle is divided, the whole is the sum of the parts.
∠DAB +∠CAD = ∠CAB
∠DAB +30° = 78°
∠DAB = 48° . . . . . . . . . . subtract 30°
_____
Alternate solution
The sum of angles in a triangle is 180°, so ...
60° +78° +∠B = 180°
∠B = 180° -138° = 42°
∠DAB = 90° -42° = 48° . . . . . acute angles in a right triangle
