Hi Shamsher,
Triangle ADE mein agar mein perpendicular banaunga point E se, toh EN hoga.
Toh line AD ka perpendicular EN hai.
Ab line AB ka perpendicular bhi EN hoga, kyunki AD ko lamba kar kay AB banaya hai.
Ab agar point E se BD kay perpendicular line banau, toh woh EN hi hogi, kyunki BD ko lamba karkay AB banta hai, aur AB ka perpendicular EN hai.
Hence, EN is the altitude of triangle BDE.
Written on Feb. 13, 2017, 8:41 p.m.