1/x+1/y=3
x+y=3xy
x+y+3xy+3y^2=3xy+3xy+3y^2=6xy+3y^2
x+y+3xy+3y^2/ 2xy+y^2=6xy+3y^2/2xy+y^2+3
1-3x·1/1-3y
=1-3x-3y+9xy=1-9xy+9xy=1
1/1-3x·1/1-3y
=1/1
=1