Factorise 25k^2-20+(4/k^2)

Answer 1

I suspect a perfect square, since I noticed that the first and last terms are perfect squares, so my suspicion points to
(5k ..... 2/k)^2
the middle term is negative, so I guess at
(5k - 2/k)^2

check:
(5k - 2/k)(5k - 2/k)
= 25k^2 -10k/k - 10k/k + 4/k^2
= 25k^2 - 20 + 4/k^2 , I was right.