The Given Factor is a Perfect Square Trinomial so the solution you'll gonna used is the PST Factor
[tex] 4 x^{2} -28 x+49 =(2 x-7)^{2} \\ [/tex]
We will Check If the answer is correct by using FOIL Mathod
[tex](2 x)(2 x)=4 x^{2} \\ \\ (2 x)(-7)=-14 \\ \\ (-7)(2 x)=-14 \\ \\ (-7)(-7)=49[/tex]
Truly;
[tex]4 x^{2} -28 x+49=(2 x-7)(2 x-7)[/tex]