Class 9 Maths — Chapter 7: TRIANGLES

What you'll learn

• ▸Concept of Congruent Figures
• ▸Congruence of Triangles and CPCT
• ▸SAS (Side-Angle-Side) Congruence Rule
• ▸Application of SAS Rule in Proofs
• ▸Invalidity of SSA/ASS Rule
• ▸ASA (Angle-Side-Angle) Congruence Rule

Chapter Summary

--- PAGE 1 --- CHAPTER 7 TRIANGLES 7.1 Introduction You have studied about triangles and their various properties in your earlier classes. You know that a closed figure formed by three intersecting lines is called a triangle. (‘Tri’ means ‘three’). A triangle has three sides, three angles and three vertices. For example, in triangle ABC, denoted as ∆ABC (see Fig. 7.1); AB, BC, CA are the three sides, ∠ A, ∠ B, ∠ C are the three angles and A, B, C are three vertices. In Chapter 6, you have also studied some properties of triangles. In this chapter, you will study in details about the congruence of triangles, rules of congruence, some more properties of triangles and inequalities in a triangle. You have already verified most of these properties in earlier classes. We will now prove some of them. A B C Fig. 7.1 7.2 Congruence of Triangles You must have observed that two copies of your photographs of the s…

Practice Questions from this Chapter

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1. Show real-world congruent objects. Get Solution →
2. Identify triangles in famous buildings. Get Solution →
3. Explain why triangles are strong. Get Solution →
4. According to the text, what is a closed figure formed by three intersecting lines called? Get Solution →
5. What does the term 'congruent' mean for geometric figures? Get Solution →
6. What does the abbreviation 'CPCT' stand for? Get Solution →
7. What is the first criterion for congruence of triangles mentioned in the text, also known as Axiom 7.1? Get Solution →
8. If triangle PQR is congruent to triangle ABC, how is it written in symbolic form? Get Solution →

Did you know?

• 💡 The strongest shape in engineering is the triangle, often seen in bridges.
• 💡 Ancient Egyptians used triangles to build the massive pyramids thousands of years ago.
• 💡 The earliest known use of congruence was for making identical bricks in ancient times.
• 💡 Some musical instruments, like triangles, are named after their simple geometric shape.
• 💡 A secret message can be hidden by dividing an image into congruent triangular pixels.

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