A ladder 15 m long reaches a window which is 9 m above the ground on one side of a street. Keeping its foot at the same point, the ladder is turned to the other side of the street to reach a window 12 m high. Find the width of the street.
Sol.Let AB be the street and let C and D be the windows at heights of 9 m and 12 m respectively from the ground.
Let E be the foot of the ladder. Then EC and ED are the two positions of the ladder.
Clearly AC = 9 m, BD = 12 m, EC = ED = 15 m and ∠CAE = ∠DBE = 90°