Sides AB and AC and median AD of atriangle ABC are respectivelyproportional to sides PQ and PR andmedian PM of another triangle PQR.

Show that Δ ABC ~ Δ PQR

Given that,


Let us extend AD and PM up to point E and L respectively, such that AD = DE and PM = ML. Then, join B to E, C to


E, Q to L, and R to L


We know that medians divide opposite sides.


Hence, BD = DC and QM = MR


Also, AD = DE (By construction)


And, PM = ML (By construction)



In quadrilateral ABEC,


Diagonals AE and BC bisect each other at point D.


Therefore,


Quadrilateral ABEC is a parallelogram.


AC = BE and AB = EC (Opposite sides of a parallelogram are equal)


Similarly, we can prove that quadrilateral PQLR is a parallelogram and PR = QL, PQ = LR


It was given in the question that,





ΔABE ΔPQL (By SSS similarity criterion)


We know that corresponding angles of similar triangles are equal


BAE = QPL (i)


Similarly, it can be proved that


ΔAEC ΔPLR and


CAE = RPL (ii)


Adding equation (i) and (ii), we obtain


BAE + CAE = QPL + RPL


⇒∠CAB = RPQ (iii)


In ΔABC and ΔPQR,


(Given)


CAB = RPQ [Using equation (iii)]


ΔABC ΔPQR (By SAS similarity criterion)


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