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Feb
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reviewed Reject suggested edit on Proof that the product of two differentiable functions is differentiable
Dec
25
reviewed No Action Needed Specific example of a quotient group
Dec
25
awarded  Nice Answer
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awarded  Nice Question
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awarded  Self-Learner
Nov
20
comment If $L = \lim_{t\to \infty}f(t)$ prove that $\lim_{t\to \infty}(1/t)\int_0^tf(x)dx = L$
possible duplicate of Proving The Average Value of a Function with Infinite Length
Nov
14
comment Product of positive definite matrices not itself positive definite
You should write out the steps in your second last paragraph and see if they actually work.
Oct
2
comment Relating Two Inner Products Without Orthogonal Basis
There is no unique choice for $T$. You would expect that an arbitrary choice (e.g. choice of basis) has to be made at some point.
Sep
28
comment How to prove $(1+x)^n\geq 1+nx+\frac{n(n-1)}{2}x^2$ for all $x\geq 0$ and $n\geq 1$?
$k+\frac{k(k-1)}{2}=\frac{(k+1)k}{2}$
Sep
20
answered a - b > 0 algebra correction
Aug
22
comment Equation of first variation for a flow
You know how to do the question now.
Aug
22
comment Equation of first variation for a flow
It is equal to $D_x(F\circ\phi)$.
Aug
22
comment Equation of first variation for a flow
1. en.wikipedia.org/wiki/Symmetry_of_second_derivatives 2. $\frac{\partial}{\partial t} \phi(\mathbf{x},t) = \mathbf{F}(\phi(\mathbf{x},t))$.
Aug
22
comment Equation of first variation for a flow
1. What do you know about functions that are of class $C^2$? 2. What is the definition of flow?
Aug
22
answered Equation of first variation for a flow
Aug
18
comment Why should the substitution be injective when integrating by substitution?
You are correct. The formula only requires that $\phi$ be continuously differentiable.