#### Answer

$\frac{49}{4}$; $(x-\frac{7}{2})^2$

#### Work Step by Step

To complete the square, add a term that is the square of half the coefficient of $x$ in the middle term. Then factor by trial and error.
$x^2-7x$
$(-\frac{7}{2})^2=\frac{49}{4}$
$x^2-7x+\frac{49}{4}$
$(x-\frac{7}{2})^2$