數學的難題？

Q: (h^4-k^4)/[2hk(h+k)²] ÷ 2(h-k)²/[(h-k)²-(h+k)²]

Sol:

(h^4-k^4)/[2hk(h+k)²] ÷ 2(h-k)²/[(h-k)²-(h+k)²]

＝ (h²-k²)(h²+k²)/[2hk(h+k)²] × [(h-k)²-(h+k)²]/[2(h-k)²]

＝ (h²-k²)(h²+k²)/[2hk(h+k)²] × (h-k-h-k)(h-k+h+k)/[2(h-k)²]

＝ (h²-k²)(h²+k²)/[2hk(h+k)²] × (-2h)(2k)/[2(h-k)²]

＝ (-4hk)(h²-k²)(h²+k²)/[4hk(h+k)²(h-k)²]

＝ (-4hk)(h²-k²)(h²+k²)/[4hk(h²-k²)²]

＝ - (h²+k²)/(h²-k²)

＝ (k²+ h²)/(k²-h²)

Ans: (k²+ h²)/(k²-h²)

ans: -(h^2-k^2)/(h-4)^2