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Suppose $M$ is a two-dimensional manifold with metric $\bar{g}$, and $r: M \to \mathbb{R}^3$ is a (not necessarily isometric) embedding of $M$ into $\mathbb{R}^3$ with first fundamental form $g$ and second fundamental form $b$.

I know that $$\operatorname{tr}(g^{-1}b)N = \Delta_g r,$$ where $N$ is the (Euclidean) surface normal of $r(M)$, and $\Delta$ is the Laplace-Beltrami operator on $M$ with respect to the pullback metric $g$.

Does a similar relationship hold for the original metric $\bar{g}$, i.e. is it true that $$\operatorname{tr}(\bar{g}^{-1}b)N = \Delta r,$$ possibly for a different interpretation of $N$?

user7530
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  • The problem here is that the second fundamental form is not an intrinsic quantity of the surface (like the Gauss Curvature), rather it is derived from the embedding. Therefore it will be difficult to give ${\bar g}^{-1}b$ a (geometric) meaning. – Thomas Apr 10 '14 at 22:33

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