Converse Mid Point Theorem


 
 
Concept Explanation
 

Converse Mid Point Theorem

Converse of Mid Point Theorem : The line drawn through the mid-point of one side of a triangle, parallel to another side, intersects the third side at its mid-point.

GIVEN  large Delta ABC in which D is the mid-point of AB and large DEparallel BC.

To Prove  E is the mid-point of AC.

Construction : Assume F to be mid point of AC. Join DF

PROOF  As we have assumed F to be the mid-point of AC.

Now, in large Delta ABC, D is the mid-point of AB          [Given]

and F is the mid-point of AC. Therefore, by Mid Point Theorem, we have

        large DFparallel BC                         .....(i)

But we are given that ,  large DEparallel BC                          ......(ii)

From (i) and (ii) , we find that two intersecting lines DE and DF are both parallel to line BC.

This is a contradiction to the parallel line axiom.

So, our supposition is wrong. Hence, E is the mid-point of AC.

Illustration:In the figure l,m and n are parallel lines intercepted by two transversal p and q such that l,m and n cut-off equal intercepts AB and BC on p. Show that l,m and n cut off equal intercepts DE and EF on q.

Solution: Join AF meetin BE at G

In Delta ACF

B is the mid point of AC and BG || CF because it is given that m and n are parallel.

By Converse of Mid Point Theorem

 G is the mid point of AF

  In Delta AFD

  G is the mid point of AF  and GE || AD  because it is given that l and m are parallel.

By Converse of Mid Point Theorem

 E is the mid point of DF

Hence DE = EF

 

Sample Questions
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Question : 1

The converse of mid-point theorem states that :

Right Option : A
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Question : 2

S and Q are the mid-point of AD and BC respectively. So, parallel line to AC must intersect for both S and Q at the mid-points of ____ and ____.

Right Option : B
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Explanation
Question : 3

E is the midpoint of median AD of DeltaABC and BE is produced to meet AC at F. If AC = 30 cm, then find AF.

 

Right Option : C
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Explanation
 
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