11. If the function $f(x)=\lg \left(\sqrt{x^{2}+2}+a x\right)-\lg b$ is an odd function defined on $\mathbf{R}$, then the value of the real number $a$ is $\qquad$ , and the value of $b$ is $\qquad$ .
11. $a= \pm 1, b=\sqrt{2} . f(0)=0, f(-1)=-f(1)$, using the method of undetermined coefficients.