Question 671642
Given
(1) (x^4 - y^4), which is the difference of two perfect squares, so we can factor it into the product of the sum and difference or
(2) (x^2 + y^2)*(x^2 - y^2)
The first factor cannot be factored unless you use imaginary numbers. The second factor, however, is again the difference of two perfect squares and will factor to give your final answer
(3) (x^2 + y^2)*(x + y)*(x - y).