3根号18+5分之1根号50-4根号2分之1
=3×根号(9×2)+5分之1根号(25×2)-4根号(4分之2)
=3×3根号2+5分之1×5根号2-4×(2分之1)根号2
=9根号2+根号2-2根号2
=8根号2