Intereting Posts

Prob. 10 (d), Chap. 6, in Baby Rudin: Holder's Inequality for Improper Integrals
The tree property for non-weakly compact $\kappa$
When you divide the polynomial $A(x)$ by $(x-1)(x+2)$, what remainder will you end up with?
Integral equal $0$ for all $x$ implies $f=0$ a.e.
The number $2^{29}$ has exactly $9$ distinct digits. Which digit is missing?
Can someone give me an example of how to work out an exact linear second order differential equation?
Why does gradient ascent/descent have zig-zag motion?
Every power series is the Taylor series of some $C^{\infty}$ function
How prove this limit $\displaystyle\lim_{n\to \infty}\frac{n}{\ln{n}}(1-a_{n})=1$
Prove that if a product$ AB$ of $n\times n$ matrices is invertible, so are the factors $A$ and $B$.
Difference between Probability and Probability Density
Game Theory Optimal Solution to 2 Player Betting Game
How to solve this determinant
Proving the inequality $|a-b| \leq |a-c| + |c-b|$ for real $a,b,c$
Is this a valid proof of $\lim _{n\rightarrow \infty }(1+\frac{z}{n})^n=e^z$?

My linear algebra notes state the following lemma: If $(v_1, …,v_m)$ is linearly dependent in $V$ and $v_1 \neq 0$ then there exists $j \in \{2,…,m\}$ such that $v_j \in span(v_1,…,v_{j-1})$ where $(…)$ denotes an ordered list.

But if at least one $v_i$ is $\neq 0$ then the list can be reordered and the lemma applied. Is $v_1 \neq 0$ just another way of saying $v_i \neq 0$ for at least one $i$?

- Derivative of Determinant Map
- $f(a+b)=f(a)+f(b)$ but $f$ is not linear
- characteristic polynomial of companion matrix
- Properties of invertible matrices
- Prove determinant of $n \times n$ matrix is $(a+(n-1)b)(a-b)^{n-1}$?
- Is there a quick proof as to why the vector space of $\mathbb{R}$ over $\mathbb{Q}$ is infinite-dimensional?

- $A \in M_3(\mathbb Z)$ be such that $\det(A)=1$ ; then what is the maximum possible number of entries of $A$ that are even ?
- Why is the 'change-of-basis matrix' called such?
- Finding Boolean/Logical Expressions for truth tables in algebraic normal form(ANF)
- Approximate spectral decomposition
- General Steinitz exchange lemma- Proof Help
- Linear Transformations: Proving 1 dimensional subspace goes to 1 dimensional
- Prove $\ker {T^k} \cap {\mathop{\rm Im}\nolimits} {T^k} = \{ 0\}$
- Understanding vector projection
- Taking powers of a triangular matrix?
- Eigenvalues of a symmetric matrix with Lagrange multipliers

Your book is correct, but silly. It should not have excluded $v_1=0$, but allowed $j=1$ instead. By convention $\operatorname{span}()=\{0\}$ (it is important that the span of *every* set of vectors is a subspace, so the empty set should give the null subspace), and $v_1=0$ (which all by itself makes the set linearly dependent) would not be an exception, because one can then take $j=1$ (and if there is no linear dependence among the remaining vectors, one *has to* take $j=1$). So it is just another case of unfounded fear of the void.

The result states (or should) that given an ordered sequence of linearly dependent vectors, there is always one of them that is in the span of set of vectors preceding it. This is always true. Indeed, you can always take the this vector to be the first one to make the sequence-up-to-there linearly dependent. The empty sequence is always independent, and a sequence with one vector is linearly dependent only if that vector is zero, in which case it is in the (empty) span of the (empty) set of preceding vectors. If the first is not zero but after some independent vectors a zero vector comes along, then it also in the span of the set of preceding vectors, but that span now has positive dimension. Of course a *nonzero* vector in the same span, in place of that zero vector, would also have made the sequence dependent; this is in fact the more common case.

$v_1\ne0$ simply means that $v_1\ne 0$. All other $v_j$ may be zero.

Note that $v_1$ does play a special role insofar as it is the only of the given vectors that is definitely in all $\operatorname{span}(v_1,\ldots, v_{j-1})$ of the claim. Note that the claim as stated fails if $v_1=0$ and $v_2,\ldots, v_m$ are linearly independant.

You can *apply* the theorem to different permutations of the $v_i$. But note that the claim differs if you permute the vectors! What you get is that *some* vector is a linear combination of the others (and that holds even if all vectors are zero). The theorem at hand is concerned with a given *ordered* seqeuence of vectors and want a vector to be a linear combination of *preceeding* vectors.

You’re essentially correct. But it’s another way of saying $v_i\neq 0$ for some $v_{i}$, not all $v_{i}$.

- Intersection of sets of positive measure
- For what $n$ is it true that $(1+\sum_{k=0}^{\infty}x^{2^k})^n+(\sum_{k=0}^{\infty}x^{2^k})^n\equiv1\mod2$
- Riemann Integral as a limit of sum
- The class of equivalence.
- Proof for $-\sup(A) = \inf(-A)$
- Correct definition of bilinear(multilinear) maps over noncommutative rings
- What is the function given by $\sum_{n=0}^\infty \binom{b+2n}{b+n} x^n$, where $b\ge 0$, $|x| <1$
- Calculating conditional entropy given two random variables
- $A \in Gl(n,K)$ if and only if $A$ is a product of elementary matrices.
- Topological groups are completely regular
- How do you find the value of $\sum_{r=0}^{44} \tan^2(2r+1)$?
- Integrable function $f$ on $\mathbb R$ does not imply that limit $f(x)$ is zero
- Entire function vanishing at $n+\frac{1}{n}$ for $n\geq 1$.
- A Borel set whose projection onto the first coordinate is not a Borel set
- Expected Values of Operators in Quantum Mechanics