Jack M. answered 12/16/12
Keys to Chemistry, Calculus, Literature and More
Assuming that the house is perpenidcular to the ground on which the ladder stands, use the Pythagorean Theorem for the sides of right triangles:
a2 + b2 = c2
In this problem a = 18, b is the unknown, and c is the length of the ladder (the hypotenuse of the triangle).
182 + b2 = 222 or
b2 = 222 - 182
b2 = 484 - 324
b2 = 160
b = √160 = 12.6 ft.
(It would be hard to climb that ladder because it is farther away from the wall than the height of the place where it touches the house)