Hello from MrBillDoesMath
Answer: 6.2 feet
Discussion:
The ladder and the wall form a right triangle. The length of the ladder, 20 in this case, is the hypotenuse of the triangle. Let "x" be the distance between the foot of the ladder and the building. Then from trigonometry,
cos (@) = length of adjacent side/ hypotenuse
or in our case
cos(72) = x / 20 => (multiply both sides by 20)
20 * cos(72) = x.
Using a calculator this becomes
20 * ( .3090) = 6.18 feet (approx) or 6.2 feet , rounded to the nearest foot.
Thank you,
Mr. B