Q1
What is the sum of a triangle's interior angles?
A180°
B90°
C360°
D270°
SSCClass 9 (SSC)Mathematics - Geometry (भूमिती)Ch 3 · Topic 1
Triangles
Triangles have three sides and angles, and understanding their properties, including congruence and inequalities, is essential in geometry.
Core concept
The sum of the interior angles of any triangle is always 180°, a fundamental property used to find missing angles.
How it works
An exterior angle of a triangle equals the sum of the two non-adjacent interior angles, a useful property for solving problems.
Why it matters
Triangle inequality theorem states that the sum of any two sides of a triangle must be greater than the third side.
Key detail
Congruent triangles have all corresponding sides and angles equal, proven through criteria like SSS, SAS, ASA, and RHS.
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Keywords worth remembering
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Quick notes
• Sum of triangle's interior angles = 180°.
• Exterior angle = sum of two non-adjacent interior angles.
• Triangle inequality: sum of two sides > third side.
• Congruent triangles: all corresponding parts equal.
• Proven via SSS, SAS, ASA, RHS criteria.
• These properties solve triangle problems.
• They're fundamental to geometry proofs.
• Practice builds proof-writing skills.