Because the Pythagorean Theorem states that a^2 + b^2 = c^2 you can say a is the distance to the north plane, and b is the distance to the east plane, while c is the distance between them. You can solve for c by plugging in and getting 2*sqrt(313).If you take the derivative of both sides, you get 2a*a' + 2b*b' = 2c*c' . by plugging in a, a' (which is the speed of the southbound plane), b, b'(speed of the westbound plane), and c, you then get 10348 + 7776 = 4*sqrt(313)*c' simplifying you get 4531=sqrt(313)c' and 4531/sqrt(313) = c' or the rate c the distance between the planes changes, so the answer is 4531/(sqrt(313)).
