Triangles
Uttarakhand Board · Class 9 · Mathematics
Quick revision notes for Triangles — Uttarakhand Board Class 9 Mathematics. Key concepts, formulas, and definitions for last-minute revision.
Key Topics to Revise
Congruence of Triangles
- Two figures are congruent if they have the same shape and size
- Congruent triangles can be placed on each other to cover completely
- When ΔABC ≅ ΔPQR, corresponding parts are equal (CPCT)
Criteria for Congruence of Triangles
- One side or one angle equality is not sufficient for congruence
- SAS (Side-Angle-Side): Two sides and included angle must be equal
- ASA (Angle-Side-Angle): Two angles and included side must be equal
Properties of Isosceles Triangles
- Isosceles triangle has two equal sides
- Angles opposite to equal sides are equal (base angles)
- Converse: If two angles are equal, opposite sides are equal
Proof Techniques and Applications
- ASA theorem proof uses SAS axiom
- Construction method for proving SSS congruence
- Indirect proof method (assuming opposite)
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Triangles covers several key topics that are frequently asked in Uttarakhand Board Class 9 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
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Start by understanding all key concepts. Practise previous year questions from this chapter. Revise formulas and definitions regularly. Use flashcards for quick revision before the exam.
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