\( \sqrt{\frac{1}{25}x^4y^8} \) при \(x=5, y=2\);

\( \sqrt{\frac{1}{25}x^4y^8} = \sqrt{\frac{1}{25}(5^4)(2^8)} = \sqrt{\frac{1}{25}625 \cdot 256} = \sqrt{6400} = 80.\)