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