To answer this, use Pythagoras' Theorem. His theorem states that, in a right angled triangle, a² + b² = c² i.e. the squares of the two shorter sides sum to the square of the hypotenuse. The path cutting straight through the rectangular park creates a right angled triangle, with the two shorter sides being two adjacent edges of the park and the hypotenuse being the path itself. Since a² + b² = c², we can substitute the values of 2 and 1.4 into a and b. 2² + 1.4² = c². Now work out what 2² + 1.4² is.
2² + 1.4² = 4 + 1.96 = 5.96
Now that we know that the length of the path squared is 5.96, we can take the square root of that to find the path's length.
√5.96 ≈ 2.44
Now put the units back in.
Solution: 2.44km