Question:
In ∆ABC, the bisector of ∠B meets AC at D. A line PQ ∥ AC meets AB, BC and BD at P, Q and R respectively.
Show that PR × BQ = QR × BP.
Solution:
In triangle BQP, BR bisects angle B.
Applying angle bisector theorem, we get:
$\frac{Q R}{P R}=\frac{B Q}{B P}$
$\Rightarrow B P \times Q R=B Q \times P R$
This completes the proof.