(t-1)(t+1) = t^2-1 through the difference of squares rule
So,
(t-1)(t+1)(t^2+1)
(t^2-1)(t^2+1)
(x-1)(x+1) ... let x = t^2
x^2-1 .... another application of the difference of squares rule
(t^2)^2 - 1... plug in x = t^2
t^4 - 1
