r) \( (5 y-4 x)^{2} \)

Did you know that the expression \( (5y - 4x)^{2} \) can represent the area of a square whose side length is \( 5y - 4x \)? When you square it, you not only find the area but also derive interesting properties of polynomials! To expand \( (5y - 4x)^{2} \), just apply the formula \( (a - b)^{2} = a^{2} - 2ab + b^{2} \). Here, with \( a = 5y \) and \( b = 4x \), you get \( 25y^{2} - 40xy + 16x^{2} \). This fundamental technique reveals how beautifully simple polynomial expressions can come together!