Let \( \cfrac{a}{b}=\cfrac{b}{c}=\cfrac{c}{d}=k \) [where \( k \) is a nonzero constant]. \(\therefore a=bk, b=ck, c=dk\) \(\therefore b=dk\times k=dk^2, a=dK^2\times k =dk^3\) Now, the left-hand side (LHS): \(=(a^2-b^2 )(c^2-d^2 )\) \(=\{(dk^3)^2-(dk^2)^2\}\{(dk)^2-d^2\}\) \(=\{d^2k^6-d^2k^4\}\{d^2k^2-d^2\}\) \(=d^2k^4(k^2-1)\times d^2(k^2-1)\) \(=d^4k^4(k^2-1)^2\) Now, the right-hand side (RHS): \(=(b^2-c^2)^2\) \(=\{(dk^2)^2-(dk)^2\}^2\) \(=\{d^2k^4-d^2d^2\}^2\) \(=\{d^2k^2(k^2-1)\}^2\) \(=d^4k^4(k^2-1)^2\) \(\therefore\) LHS = RHS [Proved].