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source: ncert
topic: geometry
class_level: class_7
chapter: ch6
difficulty: beginner
---
Class 7 | Ch6: Triangle Properties
Angle sum property: A+B+C=180° for any triangle.
Exterior angle = sum of two remote interior angles (not all three).
Triangle inequality: sum of any two sides > third side.
Pythagoras: c^2=a^2+b^2 where c=hypotenuse (opposite 90°, always longest).
Triplets: (3,4,5),(5,12,13),(8,15,17),(7,24,25).
Converse: if a^2+b^2=c^2 then right-angled.
Median: vertex to midpoint of opposite side. 3 medians meet at centroid.
Altitude: perpendicular from vertex. 3 meet at orthocentre.
Example: A=50°,B=70°,C=60°. Exterior at C=120°=A+B=50+70 verified.
Sides 9,40,41: 81+1600=1681=41^2 → right triangle. |