x(x-y)+a(x-y)

To simplify the expression \( x(x - y) + a(x - y) \), you can factor out the common term \( (x - y) \):

\[ x(x - y) + a(x - y) = (x - y)(x + a) \]

So, the simplified expression is:

\[ (x - y)(x + a) \]