c) \( (2 x-\sqrt{y})(2 x+\sqrt{y}) \)

This expression represents a difference of squares! When you see the format \( (a-b)(a+b) \), you can simplify it as \( a^2 - b^2 \). Here, you can set \( a = 2x \) and \( b = \sqrt{y} \). That means \( (2x - \sqrt{y})(2x + \sqrt{y}) = (2x)^2 - (\sqrt{y})^2 = 4x^2 - y \). Magic of algebra at work! This concept can be handy in various real-world situations, such as simplifying equations in physics problems or optimizing areas in engineering designs. For example, when calculating the area of a rectangle versus a square, applying the difference of squares could lead you to an elegant solution. It's a powerful tool that can save time and space in your calculations!