Question

I do not understand where the circled 3 comes from in the attached photo. The answer key is seeking to simplify f''(x), but I can't determine how they arrived at the answer.

Answer 1

Here is the photo I meant to attach.

Answer 2

Notice that the denominator changed from 3 to 9 on side. They factorised 3 from the first (x^2 -1)^2/3

Answer 3

My roommate just explained that, thanks @Shadowys. Basically, for someone else who comes along to read this, they multiplied by 1 in the form of 3/3. That's where the 2/9 comes from, it also cancels the 2/3 in the numerator (to create the 4x^2) and creates the 3 that I was puzzled over. Thanks!