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12h
revised Indicator function property
format cleanup
1d
comment The set of differentiable functions such that $f'(2)=b$ is a linear subspace if and only if $b=0$??
With the various edits, it's hard to tell exactly what you're asking, at this point. As for why $f'(2)=0$ rather than $f'(x)=0$ for all $x\in (0,3),$ note that the latter set is simply a subset of the former set. The same result holds there.
1d
revised Determine if a function is a metric
edited title
Jan
13
revised Find the rotation axis and angle of a matrix
deleted 2 characters in body
Jan
5
comment How to interpret some matrix lemmas on Wikipedia - the number 1 vs. the matrix I
I don't see that formula anywhere on the Sherman-Morrison formula page on Wikipedia. Could you have typed something incorrectly?
Jan
5
comment How to interpret some matrix lemmas on Wikipedia - the number 1 vs. the matrix I
Okay, if $[I]$ is the identity matrix, then what is $I$? If they are the same thing, why would we write $a[I]$ in one place, but $aI$ in another?
Jan
5
comment How to interpret some matrix lemmas on Wikipedia - the number 1 vs. the matrix I
Also, please provide a link to the article in question, for reference.
Jan
5
comment How to interpret some matrix lemmas on Wikipedia - the number 1 vs. the matrix I
Well, what does $[I]$ mean? Seems like that's relevant.
Jan
5
comment Is it true that $\int_{a}^b h^2=0\implies h=0$?
@John: A counterexample to what? The claim is that $\int_a^bh^2=0\implies h=0,$ if $h$ is continuous.
Jan
5
answered Is it true that $\int_{a}^b h^2=0\implies h=0$?
Jan
5
comment Problem with Tangent of an Angle
Well, there's nothing wrong with your math, so I'd suspect that it's either the code or one of the programs you're using.
Jan
5
comment Problem with Tangent of an Angle
The word "debugging" makes me think that you're using some sort of program to simulate the launch. It's possible that there is some error in your code that was somehow doubling the angle after it was input, but that's impossible for anyone here to say as it stands. You should probably post your old code and describe the program you're using. Hopefully someone will be able to help you figure out the issue.
Jan
5
revised How to identify an error in a proof?
added 28 characters in body
Jan
5
revised How to identify an error in a proof?
added 678 characters in body
Jan
5
answered How to identify an error in a proof?
Jan
2
revised Counting number of ways in poker game
added 6 characters in body
Jan
2
awarded  Convention
Dec
28
comment Degree of field extension is infinite
@Mary: Yes, that is what it means. Do you know why a finite extension of $\Bbb Q$ is a finite-dimensional vector space over $\Bbb Q$?
Dec
25
answered How does $\dim \mathbb C$ work?
Dec
23
comment If $f$ is entire and $e^f$ is constant $f$ is constant
Indeed, you are!