Answered

Mark leaned a 12 foot ladder against the side of his house.The bottom of the ladder was 4 feet from the house. How far up the house was the top of the ladder?



Answer :

AL2006

If you stand over there at the end of the house and look back here
at the ladder, you'll see that what Mark has is a right triangle. 

There's a right angle where the side of the house meets the ground,
the base of the triangle is the 4 feet, and the ladder is the hypotenuse.
So we know that

 (length of the ladder)² = (4-ft)² + (height of the top of the ladder)²

         (12-ft)²              = (4-ft)² + (height of the top of the ladder)²

         (144 ft²)  =  (16 ft²) + (height of the top of the ladder)²

Subtract  16ft²  from each side, and you have:

           128 ft² = (height of the ladder)²

Take the square root of each side:

           Height of the ladder = √(128 ft²)  =  11.31 ft.  (rounded)