Answer:

Step-by-step explanation:
Let L be the length of the ladder,
Given,
x = the distance from the base of the ladder to the wall, and t be time.
y = distance from the base of the ladder to the wall,
So, by the Pythagoras theorem,

,
Differentiating with respect to time (t),




Here,

Also,
( Ladder length = constant ),




Which is the required notation.