Concept:Use the identity a2−b2=(a+b)(a−b) after regrouping terms.Explanation:First, rewrite the expression: 49−x2−y2+2xy=49−(x2+y2−2xy).Notice x2+y2−2xy=(x−y)2. So the expression becomes 49−(x−y)2.Write 49 as 72. Now we have 72−(x−y)2.Apply a2−b2=(a+b)(a−b) with a=7 and b=(x−y).Thus, (7+(x−y))(7−(x−y))=(7+x−y)(7−x+y).Answer:(7+x−y)(7−x+y) – Option D.