2√50+3√75-20√(1/2)
=2√(25×2)+3√(25×3)-20√(2/4)
=2√(5²×2)+3√(5²×3)-20√(2/2²)
=2×5√2+3×5√2-20×√2/2
=10√2+15√2-10√2
=15√2