Page 1 - Lesson Note 2- ch 11 Triangle construction(Contruction)

SAI International School
CLASS - IX

Mathematics
Chapter-11: Construction
Lesson Notes-2

Sub Topic: Construction of Triangles

By using the properties of the triangle and the above basic constructions we can construct
triangles.

Construction 1: How to construct a triangle if its base, a base angle and sum of other two
sides are given?

Given the base BC, a base angle ∠B and the sum of other two sides AB + AC of a triangle ABC,
now we need to construct it.

Steps of Construction:
Step 1: First of all, draw the base BC and at the point B make an∠XBC equal to the given angle.
Step 2: From the ray BX, cut the line segment BD = AB + AC.
Step 3: Join DC now which make ∠DCY = ∠BDC.
Step 4: When CY intersect BX at A then it form the required triangle i.e. ABC.
Construction 2: How to construct a triangle if its base, a base angle and the difference of
the other two sides are given?

Given the base BC, a base angle i.e. ∠B and the difference of the other two sides AB – AC or AC
– AB, we need to construct the triangle ABC. There could be two cases:

Case (i): If AB > AC that is AB – AC is given.

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