For:
[tex]4x^2\text{ - 20x + 25}[/tex]We can factorize the polynomial:
[tex]\begin{gathered} (4x^2+20x+25)\cdot\frac{4}{4}\text{ = }\frac{(4x)^2-20(4x)+100}{4} \\ =\frac{(4x-10)(4x-10)}{4}\text{ = }\frac{2\cdot(2x-5)\cdot2\cdot(2x-5)}{4}=(2x-5)(2x-5) \end{gathered}[/tex]So we can rewrite the polynomial like this:
[tex]4x^2-9y-20x+25=(2x-5)^2-9y[/tex]