we have
[tex]3x^{4}-30 x^{3}+75 x^{2}[/tex]
Factor the leading coefficient
[tex]3x^{2}(x^{2}-10 x+25)[/tex]
we know that
[tex](x^{2}-10 x+25)=(x-5)^{2}[/tex]
substitute
[tex]3x^{2}(x-5)^{2}=3x^{2}(x-5)(x-5)[/tex]
therefore
the answer is
[tex]3x^{2}(x-5)^{2}[/tex]
