- A40°
- B70°
- C140°
- D50°
Step-by-Step Solution
Equal sides face equal angles, so . Then , giving .
Answer: B) 70°
In triangle ABC the tick marks show AB = AC, and ∠°. Find the angle at C.
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.
Master this chapter in 30 minutes a day.
Don't just memorise the answer — build a daily practice habit.
Practice 5 Similar Questions Free →All The Triangle and its Properties practice questions
More Class 7 The Triangle and its Properties practice
Two segments are drawn from A to side BC: the dashed segment AD, which has a right-angle…Ravi has four sticks of lengths 3 cm, 5 cm, 7 cm and 9 cm, drawn to scale. He picks any…A 13 m ladder leans against a wall. Its foot is 5 m away from the wall. How high up the…A 9 m lamp post casts a 12 m shadow on level ground. How long is the dashed sun-ray from…A rectangular park ABCD is 24 m long and 7 m wide. Meera walks straight across it along…