Two lines AB and CD intersect each other at a point O such that ∠AOC:∠AOD=5:7. Find all the angles.
Let ∠AOC=5k and ∠AOD=7k, where k is a constant.
Here ∠AOC and ∠AOD form a linear pair.
∠AOC+∠AOD=180°
5k+7k=180°
12k=180°
k=15°
∠AOC=5k=5×15=75°
∠AOD=7k=7×15=105°
Now, ∠BOD=∠AOC=75° [Vertically opposite angles]
∠BOC=∠AOD=105° [Vertically opposite angles]