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Exterior Angles
Last updated at November 7, 2025 by Teachoo
Class 7 (Ganita Prakash & Old NCERT)
Chapter 7 Class 7 - A tale of three Intersecting Lines (Ganit Prakash)
- Definition
- Constructing Equilateral Triangle
- Constructing a Triangle when its Sides are given
- Figure it out - Page 150, 151
- Are Triangles Possible for any Lengths?
- Figure it out - Page 154
- Visualising the Construction of Circles
- Figure it out - Page 156
- Triangle Inequality & Construction of Circles
- Figure it out - Page 159
- Constructing Triangle when 2 Sides and the Included Angle are given
- Constructing Triangle when 2 Angles and the Included Side are given
- Do triangles always exist?
- Sum of angles of a triangle
- Angle Sum Property
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Exterior Angles
- Constructions Related to Altitudes of Triangles
- Figure it out - Page 170, 171
Transcript
Exterior AnglesFor any triangle Interior Angles = ∠ 1, ∠ 2, ∠ 3 Exterior Angles = ∠ 4, ∠ 5, ∠ 6 Let’s do a question Find ∠ ACD, if ∠ A = 50°, and ∠ B = 60°. From angle sum property of triangle ∠ A + ∠ B + ∠ ACB = 180° 50° + 60° + ∠ ACB = 180° 110° + ∠ ACB = 180° ∠ ACB = 180° – 110° Exterior angle ∠ ACB = 70° Since BCD is a line Applying linear pair ∠ ACB + ∠ ACD = 180° 70° + ∠ ACD = 180° ∠ ACD = 180° – 70° ∠ ACD = 110° We can also write ∠ ACD = ∠ A + ∠ B Which leads us to the property Exterior Angle is sum of interior opposite angles Exterior angle
