根号下[2(6-2根号3+根号15-2根号5)]
=根号下(12-4根号下3+2根号下15-4根号下5)
=根号下(4+3+5-4根号下3+2根号下15-4根号下5)
=根号下(2²+(根号下3)²+(根号下5)²-2*2根号下3+2根号下15-2*2根号下5)
=根号下(2-根号下3-根号下5)²
=|2-根号下3-根号下5|
=根号下5+根号下3-2