BM and CN are perpendicular to a line passing through the vertex A of a triangle ABC. If L is the mid-point of BC, prove that LM = LN.
In ΔABC, BM and CN are perpendicular on a line drawn from A.
L is the mid point of BC.
ML and NL are joined.
To prove : ML = NL
Proof : In ΔBMP and ΔCNP
∠M=∠N (each 90∘)
∠BPM=∠CPN (vertically opposite angles)
∴ΔBMP∼ΔCNP (AA criterion)
∴BMCN=PMPN
Now in ΔBML and ΔLNC
BMCN (proved)
∠B=∠C (alternate angles)
(∵ Bm and CN are perpendicular on AX)
∴ΔBML∼ΔLMC
∴MLLN=BLLC
But BL =LC (CL is mid-point of BC)
∴BLLC=1⇒MLLN=1
∴ML=LN