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May
11
comment How does the differential $df$ act on an element of $T_pM$?
@Hurkyl Is it true that the space of all derivations at a point $p$ on a manifold $M$ has basis $\frac{\partial}{\partial x^i}|_p$, $1\leq i \leq n$?
May
11
comment How does the differential $df$ act on an element of $T_pM$?
@Hurkyl Thanks.
May
11
revised How does the differential $df$ act on an element of $T_pM$?
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May
11
comment How does the differential $df$ act on an element of $T_pM$?
Dear Kofi, your $X^i$ are real numbers yes?
May
11
comment How does the differential $df$ act on an element of $T_pM$?
Sorry Mariano, I realised that what was more meaningful to ask is the edited version of my question. I'm sorry; could you help me with this edited version? Thanks.
May
11
revised How does the differential $df$ act on an element of $T_pM$?
added 59 characters in body
May
11
comment How does the differential $df$ act on an element of $T_pM$?
Thanks for your answer. I forgot that the differential can also be thought of a kind of map between tangent spaces. However if now I think of $v$ as a vector on $S^2$, how do I compute this? For example, if $p$ is the south pole, then I can consider the vector $(1,1,0)$ based at $p$. How can I know what $df(v)$ is?
May
11
asked How does the differential $df$ act on an element of $T_pM$?
May
10
revised The operator in Tensor algebra.
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May
8
comment Proving that $\mathbb{Z}[x]$ and $\mathbb{Q}[x]$ are not isomorphic.
Biggest thermonuclear weapon....
May
8
awarded  Caucus
May
8
comment Proving that $\mathbb{Z}[x]$ and $\mathbb{Q}[x]$ are not isomorphic.
@MartinBrandenburg It's ok don't worry.
May
6
comment Proving that $\mathbb{Z}[x]$ and $\mathbb{Q}[x]$ are not isomorphic.
@KCd I have edited my answer.
May
6
revised Proving that $\mathbb{Z}[x]$ and $\mathbb{Q}[x]$ are not isomorphic.
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May
6
answered Proving that $\mathbb{Z}[x]$ and $\mathbb{Q}[x]$ are not isomorphic.
May
5
revised Exercise 2.4 Fulton's Algebraic Curves
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May
5
comment Exercise 2.4 Fulton's Algebraic Curves
@Sebastian Dear Sebastian, your claim is certainly true. In fact it's true not just for affine varieties but for more general algebraic subsets of $\Bbb{A}^n$.
May
5
comment Exercise 2.4 Fulton's Algebraic Curves
@Sebastian Dear Sebastian, no problems! I should say in your question above you are spot on in saying that $\Bbb{C}[x]/((x-1)(x-2))$ is finite dimensional over $\Bbb{C}$: By the Chinese remainder theorem, your ring is isomorphic to $\Bbb{C}[x]/(x-1) \times \Bbb{C}[x]/(x-2) \cong \Bbb{C} \times \Bbb{C}$ that is two dimensional over $\Bbb{C}$. Also you are right when you write that $I(\{1,2\}) = (x-1)(x-2)$. We have that $I(\{1,2\}) = I(\{1\}) \cap I(\{2\}) = (x-1) \cap (x-2) = (x-1)(x-2)$. The last equality comes from the fact that $(x-1)$ and $(x-2)$ are coprime. Regards,
May
5
revised Exercise 2.4 Fulton's Algebraic Curves
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May
5
answered Exercise 2.4 Fulton's Algebraic Curves