Respuesta :
The barn, the ground, and the ladder form a right triangle. If we represent the height on the barn by y, then the Pythagorean theorem tells us
... hypotenuse² = (side1)² + (side2)²
... (12 ft)² = (3 ft)² + y² . . . . . . . . . . . . fill in given information
... 144 ft² - 9 ft² = y² = 135 ft² . . . . . .subtract (3 ft)²
... y = 3√15 ft ≈ 11.6 ft . . . . . . . . . . . take the square root
The ladder reaches 11.6 feet high on the barn.
You have to use the Pithagorean Theorem because the ladder, the barn and the earth forms triangle. Than the wall of the barn and the earth makes a 90° angle. So the ladder is the hypotenuses and the earth and the barn wall are the catetes so you only have to do 12^2= 3^2 + x^2. x is how high on the barn the ladder reach. That's all. I hope I helped.