Calculate the symmetric difference between sets A = 1, 2, 3 and B = 3, 4, 5.

The symmetric difference of two sets $A$ and $B$, denoted as $A \Delta B$, is the set of elements that are in either $A$ or $B$, but not in their intersection. It can be calculated using the formula:

or equivalently:

Given:
$A = \{1, 2, 3\}$
$B = \{3, 4, 5\}$

$A - B$ contains elements that are in $A$ but not in $B$.

$B - A$ contains elements that are in $B$ but not in $A$.

The symmetric difference between A and B is $\boxed{\{1, 2, 4, 5\}}$.