In a lake of Bota

Let the depth of the water be BD = x cm

According to the given condition

AD = CD = (x + 2) cm because the straight lotus submerged into lake covering distance BC = 15cm

Now in right angled triangle DBC

CD = x + 2, is hypotenuse

BC = 15, is base and

BD = x, is the height which is also the depth of water

According to the Pythagoras theorem

Hypothenuse² = Base² + height²

CD² = BD² + BC²

(x + 2)² = x² + 15²

⇒ x² + 4 + 4x = x² + 225 (∵ (a + b)² = a² + b² + 2ab)

⇒ 4x = 221

⇒

⇒ x = 55.25 cm

The depth of water = 55.25cm