Basic Concepts of Geometry Workbook-2

Basic Concepts of Geometry Workbook-2

 

A triangle is a three sided closed figure

A triangle whose all the sides are unequal is called a scalene triangle. All the three angles will also be different in this case.

scalene triangle

AB ≠ BC ≠ AC

A triangle, two of whose sides are equal in length is called an isosceles triangle. In this case  two angles will be of equal measure and one will be different.

isosceles triangle

AB = AC ≠ BC

∠B = ∠ C □ ≠ ∠A

A triangle, all of whose sides are equal is called an equilateral triangle. All the three angles will be equal in this case and each of them will be of 60 degree measure.

equilateral triangle

AB = BC = AC

∠A = ∠B = ∠C = 60°

A triangle, each of whose angles is less than 90°, is called an acute angled triangle.

Acute Angle triangle

Acute Angle triangle

A triangle with one of its angle 90° is called a right angled triangle.

right triangle

A triangle with one of its angle greater than 90° is known as an obtuse angled triangle.

Obtuse Angle triangle

Obtuse Angle triangle

If a side of a triangle is produced, the exterior angle so formed is equal to the sum of two interior opposite angles.

exterior angle

∠x = ∠A + ∠B

∠A + ∠B +∠C = 180°                         ....(1)

∠C + ∠x = 180° (linear pair)              ....(2)

From (1) & (2)

∠x = ∠A + ∠B

Important : The angle opposite to biggest side is the biggest and the angle opposite to smallest side is the smallest.

 

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