Hello there!

I found a Indices/Algebra question which I think the writer has answered incorrectly. It goes like this;

On the step from last, they get a value of -2 and a positive + t ^ -2. I don't see where this has come from. When I went through this myself, I got a final answer of;

t^2 - (1 / (t^2)) + 2

who is correct?