# linear algebra – Constructing a basis that includes \$1-t^3\$ and \$1+t^3\$?

The question goes like: Construct a basis that includes $$1-t^3$$ and $$1+t^3$$ for the vector space of polynomials in variable $$t$$, where the $$degree$$ of polynomial is $$<=3$$.

So we have to construct a basis which already includes $$1-t^3$$ and $$1+t^3$$, that means we have to find just one more value. I tried some rough calculations that didn’t make much sense and got another vector as $$t^3$$. How should I go upon solving this problem?