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)