Geometry

• Triangle: A triangle is a three-sided polygon. It is the polygon with the least number of sides.

 

 

We denote this triangle as ΔPQR. Here, are the sides of ΔPQR. The points P, Q and R are the vertices of ΔPQR and the angles are ∠RPQ, ∠PQR and ∠QRP.

• A triangle can be classified on the basis of the measures of its angles and sides.

 

• Classification of triangles on the basis of the measures of its angles:

Name	Nature of the angle
Acute-angled triangle obtuse-angled triangle Right-angled triangle	Each angle is acute One angle is obtuse One angle is a right angle

 

• Classification of triangles on the basis of the lengths of its sides:

Name	Nature of the angle
Scalene triangle Isosceles triangle  Equilateral triangle	All three sides are of unequal length Any two sides are of equal length All sides are of equal length

 

• Angle sum property of triangles:

The sum of all the three interior angles of a triangle is 180°.

∴ ∠A + ∠B + ∠C = 180°

Exa…