A 13-m-long ladder reaches a window of a building 12 m above the ground. Determine the distance of the foot of the ladder from the building.

Height of the window =12m 

Length of a ladder =13m

In the figures, 

Let AB is ladder, A is window of building AC 

By Pythagoras Theorem:

 

AB² =AC² +BC²

(13) 2 =(12)² + x²

169 = 144 + x²

=169−144

=25 or x=5 

Distance between the foot of ladder and building =5m.