6. Упростите: √(16 × 42) + √(256 × 42)

\[ \sqrt{16 \cdot 42} + \sqrt{256 \cdot 42} = \sqrt{16} \cdot \sqrt{42} + \sqrt{256} \cdot \sqrt{42} = 4\sqrt{42} + 16\sqrt{42} = 20\sqrt{42}. \] Ответ: \(20\sqrt{42}\).