Class 7 Maths Part 2 Chapter 1, Geometric Twins, introduces geometric congruence—Discovering the minimum measurements needed to make an exact replica of a figure, establishing the SSS, SAS, ASA, AAS and RHS triangle congruence criteria, and proving angle properties of isosceles and equilateral triangles.
What Class 7 Mathematics Chapter 1 Covers
1.1–1.2 Geometric Twins & Congruence of Triangles explores superposition and vertex-correspondence notation ($\triangle ABC \cong \triangle XYZ$), and tests which sets of three measurements guarantee congruence: SSS, SAS (included angle), ASA, AAS and RHS (right angle, hypotenuse and side)—while showing why AAA and SSA fail.
1.3 Angles of Isosceles and Equilateral Triangles uses triangle congruence to prove that angles opposite to equal sides of an isosceles triangle are equal, and that every interior angle of an equilateral triangle measures $60^\circ$.
Exercises in Chapter 1
- Figure it Out exercise sets and Summary with geometric and algebraic puzzles.
Read Class 7 Mathematics Chapter 1 Online
More Chapters
- Next: Chapter 2: Operations with Integers
- All Mathematics chapters and the other Class 7 books: Class 7 NCERT books 2026-27
FAQ
What are the five conditions for the congruence of two triangles?
Two triangles are congruent if they satisfy SSS (Side-Side-Side), SAS (Side-Angle-Side with the included angle), ASA (Angle-Side-Angle), AAS (Angle-Angle-Side), or RHS (Right angle-Hypotenuse-Side in right-angled triangles).
Why does SSA (two sides and a non-included angle) not guarantee congruence?
Given two side lengths and a non-included acute angle, an arc can intersect the third side at two different points, producing two non-congruent triangles with the exact same SSA measurements.