y=x−12x−1=2+x−11⇒23x2+y2=23x2+(x−1)21+x−14+4,
Let f(x)=23x2+(x−1)21+x−14+4,f′(x)=3x−(x−1)32−(x−1)24, since f′(x) is monotonically increasing on (1,+∞), and f′(x)=0⇒3x=(x−1)32+4(x−1)⇒3x(x−1)3=4x−2 ⇒(x−2)(3x3−3x2+3x−1)=0⇒x=2, so f(x)min=f(2)=6+1+8=15.