In Fig. 4.142, PA, QB and RC are each perpendicular to AC. Prove that .
We have, PA ⏊ AC, and RC ⏊ AC
Let AB = a and BC = b
In ΔCQB and ΔCPA
<QCB = <PCA (Common)
<QBC = <PAC (Each 90°)
Then, ΔCQB ~ ΔCPA (By AA similarity)
So, (Corresponding parts of similar triangle area proportion)
Or, -----------(i)
In ΔAQB and ΔARC
<QAB = <RAC (Common)
<ABQ = <ACR (Each 90°)
Then, ΔAQB ~ ΔARC (By AA similarity)
So, (Corresponding parts of similar triangle area proportion)
Or, -----------(ii)
Adding equation i & ii
=
Or, y () =
Or, y () = 1
Or, =