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Finding Missing Angles
Last updated at November 7, 2025 by Teachoo
Class 7 (Ganita Prakash 1, 2 & 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
- Exterior Angles
- Constructions Related to Altitudes of Triangles
- Figure it out - Page 170, 171
Transcript
Finding Missing Angles In ∆ABC, ∠A + ∠B + ∠C = 180° 55° + 75° + ∠C = 180° 130° + ∠C = 180° ∠C = 180° − 130° ∠C = 50° (Angle sum property of triangle) Find the missing angle In ∆PQR, ∠P + ∠Q + ∠R = 180° 30° + ∠Q + 50° = 180° ∠Q + 80° = 180° ∠Q = 180° − 80° ∠Q = 100° (Angle sum property of triangle) Find the missing angle In ∆XYZ, ∠X + ∠Y + ∠Z = 180° 20° + 90° + ∠Z = 180° 110° + ∠Z = 180° ∠Z = 180° − 110° ∠Z = 70° (Angle sum property of triangle)
