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The Base Bc of Triangle Abc is Divided at D So that Bd = 1/2 Dc. Prove that Area of δAbd = 1/3 of the Area of δAbc. - Mathematics

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Question

The base BC of triangle ABC is divided at D so that BD = `1/2`DC.
Prove that area of ΔABD = `1/3` of the area of ΔABC.

Sum

Solution


In ΔABC, ∵ BD = `1/2"DC" ⇒ "BD"/"DC" = 1/2`

∴ Ar.( ΔABD ) : Ar.( ΔADC ) = 1:2

But Ar.( ΔABD ) + Ar.( ΔADC ) = Ar.( ΔABC )

Ar.( ΔABD ) + 2Ar.( ΔABD ) = Ar.( ΔABC )

3 Ar.( ΔABD ) = Ar.( ΔABC )

Ar.( ΔABD ) = `1/3`Ar.( ΔABC )

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Triangles with the Same Vertex and Bases Along the Same Line
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Chapter 16: Area Theorems [Proof and Use] - Exercise 16 (B) [Page 201]

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Selina Concise Mathematics [English] Class 9 ICSE
Chapter 16 Area Theorems [Proof and Use]
Exercise 16 (B) | Q 5 | Page 201
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