Answer
$3(x^2+1)(x+1)(x-1)$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here:
$3x^4-3=3((x^2)^2-1^2)=3(x^2+1)(x^2-1)=3(x^2+1)(x+1)(x-1)$
