Divide:
h^2-k^2/h^4-k^4
________________
h-k/h^2+k^2
type it this way:
(h^2-k^2)/(h^4-k^4) / ( (h-k)/(h^2+k^2) )
= (h^2-k^2)/(h^4-k^4)((h^2+k^2)/(h-k) )
= (h+k)(h-k)/((h^2 + k^2)(h+k)(h-k)) ((h^2+k^2)/(h-k))
= 1/(h-k) , h ≠ k
h^2-k^2/h^4-k^4
________________
h-k/h^2+k^2
(h^2-k^2)/(h^4-k^4) / ( (h-k)/(h^2+k^2) )
= (h^2-k^2)/(h^4-k^4)((h^2+k^2)/(h-k) )
= (h+k)(h-k)/((h^2 + k^2)(h+k)(h-k)) ((h^2+k^2)/(h-k))
= 1/(h-k) , h ≠ k