What is the missing constant term in the perfect square that starts with ${\mathrm{x}}^2+\mathrm{bx}?$

Given expression: ${\mathrm{x}}^2+\mathrm{bx}$

For finding the missing, we should convert it into a perfect square.

${\mathrm{x}}^2 + \mathrm{bx} = {\mathrm{x}}^2 + 2.\frac{\mathrm{b}}{2}.\mathrm{x} + {\left(\frac{\mathrm{b}}{2}\right)}^2 - {\left(\frac{\mathrm{b}}{2}\right)}^2$

Hence, from the above expression, we can conclude that the missing term is ${\left(\frac{\mathrm{b}}{2}\right)}^2$.