Class 7 Maths- Ch 6 – Triangle and its properties

Class 7 Maths- Ch 6 – Triangle and its properties

Angle Sum Property

The total measure of the three angles of a triangle is 180°.

Given: -∠1,∠2,∠3 are angles of  ∆ABC

∠4 is the exterior angle when BC is extended to D

Justification ∠1+∠2=∠4(by exterior angle property)

∠1+∠2+∠3=∠4+∠3 (adding ∠3 on both sides)

∠4 and ∠3 form a linear pair so it is 180°

Hence ∠1+∠2+∠3=180°

Watch and learn more about angle sum property – Class 7 Maths.

Two Special Triangles: Equilateral and Isosceles

Equilateral Triangle: – Triangles in which all the three sides are equal are called an equilateral triangle.

Two Important points:-

• all sides have the same length
• each angle has measure 60°

Isosceles triangle: – Triangles in which two sides are of equal lengths is called an isosceles triangle.

Two Important points:-

• two sides have the same length
• base angles opposite to the equal sides are equal

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