I was doing some problems , but I don´t know how to prove 2 of them Dx , that are about homeomorphism. I have to prove that $ R^{n + 1} - \left\{ 0 \right\} \cong S^n \times\,R $ where R denotes the real numbers all of this with the usual topology of $R^n$
For every $c>0$ $ \left\{ {\left( {x,y,z} \right) \in R^3 :x^2 + y^2 - z^2 = c} \right\} \cong S^1 \,\times\,R $ I think that it will be useful to use the last problem :/