Given Expression,
[tex] \sf \: f(x) = {x}^{2} - 10x + 25[/tex]
The above expression is of the form (a - b)² = a² - 2ab + b²
Thus,
[tex] \implies \: \sf \: f(x) = (x) {}^{2} - 2(5)x + {5}^{2} \\ \\ \implies \: \sf \: f(x) = (x - 5) {}^{2} [/tex]
Equating f(x) = 0,
[tex] \implies \: \sf \: (x - 5) {}^{2} = 0 \\ \\ \implies \: \sf \: x - 5 = 0 \\ \\ \implies \: \boxed{ \boxed{ \sf x = 5}}[/tex]