#### Answer

$-1$

#### Work Step by Step

The given equation can be written as:
$f(x)=(x^2+2x+1)+3
\\f(x)=(x+1)^2+3
\\f(x) = [x-(-1)]^2+3$
This means the given equation is equivalent to $f(x) = [x-(-1)]^2+3$.
RECALL:
The vertex form of a quadratic function is $f(x)=a(x-h)^2+k$ where $(h, k)$ is the vertex.
The function $f(x) = [x-(-1)]^2+3$ is in vertex form. The vertex is $(-1, 3)$.
Thus, the missing expression in the given statement is:
$-1$