We can use the Pythagorean Theorem to determine if the three side lengths form a right triangle. The Pythagorean Theorem states that in a right triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides.
If we let a = 6km, b = 8km, and c = 12km, we can use the Pythagorean Theorem to check if the three side lengths form a right triangle:
c^2 = a^2 + b^2
12^2 = 6^2 + 8^2
144 = 36 + 64
144 = 100
Since the equation is not true, this means that the three side lengths do not form a right triangle. Instead, they form an obtuse triangle, since one of the angles is greater than 90 degrees.