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## Homework Statement

(1)Why can't I solve [itex]x^{4}-5x^{2}+4[/itex]

in the following way:

[itex](x^{4}-4x^{2}+4)-x^{2}[/itex]

...

[itex](x^{2}-2-x^{2})(x^{2}-2+x^{2})[/itex]

...

If there is any reason why..

(2)How to solve it if the answer to get is [itex](x-1)(x+1)(x-2)(x+2)[/itex] ?