3根号20-根号45-根号1/5
=3*根号4*5-根号9*5-根号1/根号5
=3*根号4*根号5-根号9*根号5-1/根号5
=3*2*根号5-3*根号5-(根号5)/5
=6根号5-3根号5-1/5*(根号5)
=14/5*(根号5)