9514 1404 393
Answer:
115°
Step-by-step explanation:
Let A, B, C represent the vertex angle measures of ΔABC. Then the sum of angles in ΔADC is ...
A/2 +∠ADC + C/2 = 180°
Multiplying by 2 gives ...
A + C + 2×∠ADC = 360°
From the given information, we know ...
A + C + 50° = 180° . . . . . sum of angles in ΔABC
This lets us write an expression for (A +C):
A + C = 130° . . . . . . . . subtract 50° from the previous equation
Substituting for A+C, we get ...
130° + 2×∠ADC = 360°
2×∠ADC = 230° . . . . . . . . . subtract 130°
∠ADC = 115° . . . . . . . . . . . divide by 2
