Sides AB and AC and median AD of a triangle ABC are respectively proportional to sides PQ and PR and median PM of another triangle PQR. Show that $∆ABC \sim ∆PQR$.
Given:
Two triangles $ΔABC$ and $ΔPQR$ in which $AB, AC$ and median $AD$ of $ΔABC$ are proportional to sides $PQ, PR$ and median $PM$ of $ΔPQR$
$\frac{AB}{PQ} = \frac{AC}{PR} = \frac{AD}{PM}$
To do:
We have to prove that $ΔABC \sim ΔPQR$
Solution:
We have,
$\frac{AB}{PQ} = \frac{AC}{PR} = \frac{AD}{PM}$ (D is the mid-point of BC and M is the mid point of QR)
$ΔABD \sim ΔPQM$ [SSS similarity criterion]
Therefore,
$\angle ABD = \angle PQM$ [Corresponding angles of two similar triangles are equal]
$\angle ABC = \angle PQR$
In $ΔABC$ and $ΔPQR$
$\frac{AB}{PQ} = \frac{AC}{PR}$........(i)
$\angle A = \angle P$........(ii)
From above equation (i) and (ii), we get,
$ΔABC \sim ΔPQR$ [By SAS similarity criterion]
Hence proved.
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