b=(x-y) (x+y)

The expression \( b = (x - y)(x + y) \) is a product of two binomials. This expression can be simplified using the difference of squares formula, which states:

\[ a^2 - b^2 = (a - b)(a + b) \]

In your case, \( a = x \) and \( b = y \). Therefore, we can rewrite the expression:

\[ b = (x - y)(x + y) = x^2 - y^2 \]

So, the simplified form of \( b \) is:

\[ b = x^2 - y^2 \]

If you have any more questions or need further clarification, feel free to ask!