- A80°
- B55°
- C100°
- D85°
Step-by-Step Solution
In triangle ABD, the exterior angle . In triangle .
Answer: B) 55°
In triangle ABC, D is a point on and AD is joined. ∠°, ∠° and ∠BAD = 30°. Find = ∠DAC.
Class 7The Triangle and its PropertiesTriangles
Key idea: Exterior angle property
Extend one side of a triangle past a vertex. The angle formed outside the triangle is the **exterior angle** at that vertex.
**Exterior angle = sum of the two opposite interior angles.**
So if the two non-adjacent interior angles are 50° and 60°, the exterior angle = 50° + 60° = 110°.
Why? The exterior angle and the adjacent interior angle form a linear pair (sum 180°), and the three interior angles also sum to 180°. Subtract: exterior = sum of the other two interior angles.
**Exterior angle = sum of the two opposite interior angles.**
So if the two non-adjacent interior angles are 50° and 60°, the exterior angle = 50° + 60° = 110°.
Why? The exterior angle and the adjacent interior angle form a linear pair (sum 180°), and the three interior angles also sum to 180°. Subtract: exterior = sum of the other two interior angles.
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