a ladder 13m long is placed on the ground in such a way that it touches the top of a vertical wall 12m high. find the distance of the foot of the ladder from the bottom of the wall

by applying Pythagoras theorem;

the ladder (13m) acts as hypotenuse

the wall (12m) acts as height

the distance between the the two is the base

therefore

a² + b² = c²

b² = c² - a²

b² = 169 - 144

b² = 25

√b² = √25

b = 5m

the distance is 5m