[tex](5-x)(x+4)(5-x)(x+4)[/tex]
[tex] [(5-x)(x+4)]^{2} [/tex]
[tex] [- x^{2} +x+20]^{2} [/tex]
[tex] x^{4} - x^{3}-20 x^{2} - x^{3} + x^{2} +20 x-20 x^{2} +20 x+400[/tex]
[tex] x^{4}-2 x^{3} -40 x^{2} -19 x^{2} +20 x+400[/tex]
[tex] x^{4} -2 x^{3} -59 x^{2} +20 x+400[/tex]
