If a boat leaves a dock and sails 8 km north and then 13 km east, it is no longer directly north or east of the dock. Instead, it is northeast of the dock. To find the distance from the dock to the boat, you would need to use the Pythagorean theorem.
The Pythagorean theorem states that in a right triangle, the square of the length of the hypotenuse (the longest side) is equal to the sum of the squares of the lengths of the other two sides. In this case, the length of the hypotenuse is the distance from the dock to the boat, and the lengths of the other two sides are 8 km and 13 km.
If we call the distance from the dock to the boat "d," the equation that represents the Pythagorean theorem in this situation is d^2 = 8^2 + 13^2. Solving this equation, we find that d = 15 km. This means that the boat is 15 km from the dock.