6) 2√50-8√2 – 3√98

6) $$2 \sqrt{50} - 8 \sqrt{2} - 3 \sqrt{98} = 2 \sqrt{25 \cdot 2} - 8 \sqrt{2} - 3 \sqrt{49 \cdot 2} = 2 \cdot 5 \sqrt{2} - 8 \sqrt{2} - 3 \cdot 7 \sqrt{2} = 10 \sqrt{2} - 8 \sqrt{2} - 21 \sqrt{2} = (10 - 8 - 21) \sqrt{2} = (2 - 21) \sqrt{2} = -19 \sqrt{2}$$

Ответ: $$-19 \sqrt{2}$$