Spotting this when integrating

Hi - I'm struggling to spot this specific thing when I'm integrating - I've attached it below. I just don't understand what it is or where it comes from. I get that if I factorise u^2 - 4 I get (u-2)(u+2)... but even if I worked backwards, and used that to try to get to u^2/u^2-4 I don't? I get 4/u^2-4. and where's the 1 coming from? Help!!

Exam questions often suggest the substitution and with practice you will recognise when it's useful.

The 1 comes from splitting the integral into partial fractions - when the numerator and denominator have the same highest power you have to divide [like a 'top heavy' fraction.

Maybe revise partial fractions?