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Sep
29
accepted Help with a linear algebra problem; defining a function with some properties
Sep
29
comment Help with a linear algebra problem; defining a function with some properties
Well, I feel stupid now. It's $(-2,1,1)$. Everything works out now. Thanks!
Sep
29
comment Help with a linear algebra problem; defining a function with some properties
That's what you get if you solve the equations defining $f^{-1}(1,1,1)$. I don't understand your edit; $(-2,1,0)$ itself doesn't belong to $f^{-1}(1,1,1)$. You have to add $(-1,2,0)$ to it.
Sep
29
comment Help with a linear algebra problem; defining a function with some properties
I got there, but when trying to solve the system $f(x) = (1,1,1)$, I get something different than what it should be.
Sep
29
asked Help with a linear algebra problem; defining a function with some properties
Sep
28
comment How to solve $\cos(\pi/2+t)\ge 0$?
@Michael: your book has the same answer, it's just written complicated. Think about it; $t \in [\pi, 3\pi/2]$ or $t \in [3\pi/2, 2\pi]$ is the same thing as $t \in [\pi, 2\pi]$.
Sep
28
comment How do I integrate $\sqrt{x^2+81}$ using trig substitution?
Hyperbolic trig functions will work better in this case, probably.
Sep
27
answered Multivariable Partial Derivative
Sep
27
comment Multivariable Partial Derivative
Why can't you just calculate it, instead of trying to check all those options?
Sep
25
comment Solving simple modulus with a variable but use inegality operator
I don't know if you meant $1$ or $-1$, but in any case $|4x-2| \ge 1$ is equivalent to $4x-2 \le -1$ or $4x-2 \ge 1$.
Sep
25
comment Volume of a pyramid as a determinant?
@HenningMakholm: Well, it's probably a tetrahedron.
Sep
24
asked What is it called when a function is not continuous but still can have a derivative?
Sep
24
awarded  Citizen Patrol
Sep
23
comment What is the relevance of the supremum in this question?
@dukenukem: Pretty much. Sometimes the supremum is written a little differently, like this: $\displaystyle \sup_{x\in I}|f(x)-g(x)|$. But it's the same thing.
Sep
23
answered What is the relevance of the supremum in this question?
Sep
23
suggested rejected edit on How to go about solving $((1+iz)/(1-iz))^4 = 1/2 + i\sqrt3/2$?
Sep
23
comment How do you explain the appearance of a sine in the integral for calculating the surface area of a sphere?
@Tpofofn: But where does the $2$, or, if you want, the $\sin \phi$ come from?
Sep
23
asked How do you explain the appearance of a sine in the integral for calculating the surface area of a sphere?
Sep
22
comment The zero vector
If you keep the requirement that addition and scalar multiplication are closed and ask for the subspace to be non-empty, then as a consequence zero must be in it. We just include that axiom to get rid of the empty set.
Sep
21
comment Question about solving 2nd order linear differential equations
What book are you using, by the way?