(x+1)☆(1-x)=2/3
1/(x+1)-1/(1-x)=2/3
1/(x+1)+1/(x-1)=2/3
(x-1+x+1)/(x²-1)=2/3
2x/(x²-1)=2/3
x²-1=3x
x²-3x-1=0
x²-3x+9/4=1+9/4
(x-3/2)²=13/4
x-3/2=±√(13/4)
∴x=3/2±1/2√13