Question

Aratati ca x^4-5x^2+4=(x-1)(x+1)(x-2)(x+2)

Answer 1

      
$x^{4} - 5x^{2} + 4 = \\ = x^{4} - x^{2} - 4x^{2} + 4 = \\ = x^{2} (x^{2} - 1) - 4(x^{2} - 1) = \\ = (x^{2} - 1)(x^{2} - 4) = \boxed{(x-1)(x+1)(x-2)(x+2)}$