√28-√4/7 ；
=2√7-2/7√7
=12/4√7
√4/5-√5+√1/6
=2/5√5-√5 +1/6√6
=-3/5√5+1/6√6
√49/2+√108-√12
=7/2√2+6√3-2√3
=7/2√2+4√3