u=10^x, u>0,u≠1，y=(u^2 +1)/(u^2-1) +1,y-1=(u^2 +1)/(u^2-1),(y-2)u^2=y,u^2=y/(y-2),10^(2x)=y/(y-2),2x=lg[y/(y-2)],x=1/2•lg[y/(y-2)],y=1/2•lg[x/(x-2)],x<0, or x>2.
