Answer
$\bf False$.
Work Step by Step
$\bf False$.
For this equation to be separable, we would have to be able to write $x+y$ from the equation $y'=x+y$ in the form of $f(x)g(y)$, where $f(x)$ is a function of $x$ only and $g(y)$ is a function of $y$ only. Since this is impossible to write, the statement is false.
