Question 486355
Use formula {{{a^2-2ab+b^2=(a-b)^2}}}
{{{x^2-7x+__=(x-__)^2}}}
{{{x^2-2*x*(7/2)+(7/2)^2=(x-7/2)^2}}}
{{{x^2-7x+49/4=(x-7/2)^2}}}