!/7×(!/7-!/27)-!/3(!/7+!/27)
=---------------------------------------=
(!/7+!/27)(!/7-!/27)
7-!/189 -!/21-!/81
=-------------------------=
7-27
7-!/189 -!/21-9
=---------------------=
-20
-2-!/21(!/9-1)
=-----------------=
-20
-2-!/21 ×(3-1)
=----------------=
-20
=(-2-2!/21)/(-20)=-2(1+!/21)/-20=
=(1+!/21)/10