Please I'm looking for some exersices similar to this one below. I have looked in a lot of books but in vain. If some one can suggest some books or links, I would be very grateful.
Let $(M,\langle,\rangle)$ be a riemannian manifold equipped with th connexion of Levi-Civita $\nabla$.
- Show that in an orthonormal frame, $\Delta(f)=\sum_{i=1}^n Hess(f)(E_i,E_i)$
- Show that $Ric(X,Y)=\sum_{i=1}^n \langle R(X,E_i)Y,E_i\rangle$
Let $X$ be a Killing vector field on $M$, i.e., $$X\langle Y,Z\rangle -\langle [X,Y],Z\rangle -\langle Y,[X,Z]\rangle =0, $$ and let $f :M\to \mathbb R$ be a function defined by : $f(p)=\frac{1}{2} \langle X(p),X(p) \rangle $
Show that $\langle \nabla_YX,Z\rangle +\langle Y,\nabla_Z X\rangle =0.$
Show that for any function $g$, $\Delta(X(g))= X(\Delta(g)).$
Show that $\nabla f=-\nabla_XX.$
Show that $Hess(f)(Y,Y)=-\langle R(X,Y)X,Y\rangle +\langle \nabla _YX,\nabla _YX\rangle .$
Show that $\Delta(f)=-Ric(X,X)+|\nabla X|^2.$