The wall and the ground are perpendicular to each other.
Hence, the ladder leaning against the wall forms a right-angled triangle.
In ∆ABC, ∠B = 90°
According to Pythagoras’ theorem,
l(AC)2 = l(AB)2 + l(BC)2
∴ 152 = l(BC)2 + 92
∴ 225 = l(BC)2 + 81
∴ 225 – 81 = l(BC)2
∴ 144 = l(BC)2
∴ 122 = l(BC)2
∴ l(BC) = 12
∴ The distance between the base of the wall and that of the ladder is 12 m.
