Answer
$4$
Work Step by Step
With an expression that has the form $x^2 + bx$, add $(\frac{b}{2})^2$ to complete the square:
In the expression $x^2 + 4x$, $b$ is $4$; therefore, $(\frac{b}{2})^2$ is:
$(\frac{4}{2})^2$
Simplify the fraction:
$(2)^2$
Evaluate the exponent:
$4$
