Level 3 Quant Quiz

Hi,
Can anyone please help me with this question’s solution?

What’s the problem with it?

I was not able to understand the solution provided in the lesson

Can we not directly use 5 in place of the x in the function (x^2+1/x-1)?

No, because for what value of x are you actually putting 5 as the input? It’s not x = 5.