
ABCD is a trapezium in which AB || DC and E is the mid-point of AD.
Let EF intersects BD at P.
Then in ∆DAB
Through E, EP || AB intersects BD at P.
By the converse of mid-point theorem.
=> P is the mid-point of BD.
Now in ∆BCD, P is the mid-point of BD.
Through P, PF || DC intersects BC at P.
By the converse of mid-point theorem.
F is the mid-point of BC.
Hence proved.