# Extending a section to a basis of sections in a trivial bundle.

Suppose we have a manifold $M$ of dimension $m$ and let $E$ be the rank $n$ trivial vector bundle on $M$. Let $\Gamma$ be a section of the trivial bundle $E$. My question is, are there some conditions on the section $\Gamma$ which ensure that it extends to a basis of sections of the vector bundle $E$.

I know that in general this is not possible (for example in case of the trivial bundle on sphere) but I am unable to see what exactly is the obstruction.

## 1 Answer

The trivial bundle defines a line subbundle $L \subset E$; you're asking precisely that $E/L$ also be trivial. But as you point out in the question, the tangent bundle $TS^2$ plus a trivial line bundle is the trivial 3-plane bundle, so there is a line subbundle of the trivial 3-plane bundle that gives $TS^2$ as its quotient (and hence every other section of the trivial rank 3 bundle must, at some point, be a scalar multiple of our "special" one.)

• I don't quite understand your answer If I am not mistaken you seem to be answering the question when the quotient is $TS^2$ but not when is it trivial. – happymath Jun 8 '16 at 7:26
• @happymath I'm giving an example where the quotient is not trivial. Being able to extend a section to a basis of sections is the same thing as the quotient being trivial. – user98602 Jun 8 '16 at 7:27
• I am sorry for not being clear but I already know of this example that is why I wanted some conditions on section which ensure the quotient is trivial – happymath Jun 8 '16 at 7:33
• There is nothing simpler than what you and I have said. – user98602 Jun 8 '16 at 7:36
• I am looking for a condition for a vector bundle over any manifold not just the sphere – happymath Jun 8 '16 at 7:37