3. As shown in Figure 11, a shape is formed by square $ABCD$ and $\triangle BEC$, where $\angle BEC$ is a right angle. Let the length of $CE$ be $a$ and the length of $BE$ be $b$. Then the distance from point $A$ to line $CE$ is $\qquad$
As shown in Figure 11, rotate Rt $\triangle B E C$ 90 degrees clockwise around point $B$ to get Rt $\triangle A B G$.
Extend $A G$, intersecting $C E$ at point $F$. Then $A F \perp C E, A G=C E=a, B G=B E$.
Therefore, quadrilateral $B G F E$ is a square.
$$
\begin{array}{l}
\Rightarrow G F=B E=b \\
\Rightarrow A G+G F=C E+B E=a+b
\end{array}
$$
$\Rightarrow$ The distance from point $A$ to line $C E$ is $a+b$.