English

In triangle ABC, angle B is obtuse. D and E are mid-points of sides AB and BC respectively and F is a point on side AC such that EF is parallel to AB. Show that BEFD is a parallelogram.

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Question

In triangle ABC, angle B is obtuse. D and E are mid-points of sides AB and BC respectively and F is a point on side AC such that EF is parallel to AB. Show that BEFD is a parallelogram.

Sum
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Solution

The figure is shown below

AD = DB

BE = EC

EF || BD

In Δ ABC

E is the midpoint of AB and 

EF || BD

∴ By the midpoint theorem, F will be the midpoint of AC and D will be the midpoint of AB.

As D and F are midpoints of AC and AB respectively.

∴ By the midpoint theorem of DF || BC or BE

Since DF || BE and EF || BD

Hence, BEFD is a parallelogram.

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Chapter 11: Mid-point Theorem and Its Converse [Including Intercept Theorem] - Exercise 12 (B) [Page 154]

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Selina Concise Mathematics [English] Class 9 ICSE
Chapter 11 Mid-point Theorem and Its Converse [Including Intercept Theorem]
Exercise 12 (B) | Q 5 | Page 154
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