Complete question :
The latter is leaning against the building so that the distance from the ground to the top of the ladder is 9 feet less than the length of the ladder finally put the ladder in the distance from the bottom of the ladder to the building 15 feet. Find length of the ladder.
Answer:
17
Explanation:
From Pythagoras :
Hypotenus = sqrt(opposite² + adjacent²)
From the diagram
l = sqrt((l-9)² + 15²)
l² = (l² - 18x + 81 + 225)
Square both sides
l² = l² - 18x + 306
l² - l² = 306 - 18x
18l = 306
l = 306/18
l = 17