[tex]\bf (x+y)^2(x-y)^2[/tex]
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[tex]\rightarrow \sf x^4-2x^2y^2+y^4[/tex]
breakdown
[tex]\rightarrow \sf x^4-x^2y^2-x^2y^2+y^4[/tex]
factor common term
[tex]\rightarrow \sf x^2(x^2-y^2)-y^2(x^2-y^2)[/tex]
collect in groups
[tex]\rightarrow \sf (x^2-y^2)(x^2-y^2)[/tex]
apply difference between two square method: x² - y² = (x+ y)(x-y)
[tex]\rightarrow \sf (x+y)(x-y) (x+y)(x-y)[/tex]
simplify
[tex]\rightarrow \sf (x+y)^2(x-y)^2[/tex]