10. Y is two different numbers selected from the first 500 natural numbers, and X is greater than y, 1. Find the maximum value of X + Y / X-Y, 2. Find the minimum value of X + Y / X-Y

10. Y is two different numbers selected from the first 500 natural numbers, and X is greater than y, 1. Find the maximum value of X + Y / X-Y, 2. Find the minimum value of X + Y / X-Y

X + Y / X-Y = (1 + Y / x) / (1-y / x) = 2 / (1-y / x) - 1, let a = Y / x, the original formula = B, then 0 < a < 1, B = 2 / (1-A) - 1. This function is an increasing function on a ∈ (0,1),
So when a is closest to 0, the original formula is the smallest, where x = 500 and y = 1
When a is closest to 1, the original formula is the largest, where x = 500 and y = 499