Question

E and F are respectively the midpoints of non parallel sides AB and BC of a trapezium ABCD, prove that EF || AB.​

Answer 1

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• Let ABCD be a trapezium in AB || DC. Let E and F be the midpoints of AD and BC respectively E and F are joined.

We have to show that EF || AB.

If possible,let EF be not parallel to AB then draw EG || AB, meeting BC to G.

• Now, AB || EG || DC and the transversal AD cuts them at A,E,D respectively such that AE = ED.

• Also, BGC is the other transversal cutting AB,EG and DC at B, G and C respectively.

∴ BG = GC (by intercept theorem).

This shows that G is the midpoint of BC.

Hence,G must coincide with F [∴ F is the midpoint of BC].

Thus,our supposition is wrong.

Hence, EF || AB.