14h
comment A finite-dimensional $K$-algebra?
@karparvar in this case, yes.
21h
answered Can all real polynomials be factored into quadratic and linear factors?
1d
comment Is there a commutative ring $R$ with an idempotent endomorphism $f$ that cannot be expressed as $f(x)=sx$ for some idempotent $s \in R$?
@goblin I had been inconsistently thinking of R in general and as a field.
1d
revised Is there a commutative ring $R$ with an idempotent endomorphism $f$ that cannot be expressed as $f(x)=sx$ for some idempotent $s \in R$?
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1d
comment Is there a commutative ring $R$ with an idempotent endomorphism $f$ that cannot be expressed as $f(x)=sx$ for some idempotent $s \in R$?
@goblin Oh, sure I guess we need at least that R has no nilpotent elements to make the claim.
1d
answered Is there a commutative ring $R$ with an idempotent endomorphism $f$ that cannot be expressed as $f(x)=sx$ for some idempotent $s \in R$?
1d
comment What is recommended for studying Linear Algebra?
People have asked questions like this many times before: please use the search feature to try to find your question before you post
1d
comment be J be a matrix so: JJ^-1 = I and A a matrix so: A^t JA = J. prove that A is invertible so that AA^-1 = I
No property of the transpose is being used. It might perhaps be clearer if the order of the first two items in the last string of equalities were interchanged.
1d
comment be J be a matrix so: JJ^-1 = I and A a matrix so: A^t JA = J. prove that A is invertible so that AA^-1 = I
@GitGud oop, I did not see the comment claiming not to know determinants when I started writing. It is very odd, if true.
1d
comment be J be a matrix so: JJ^-1 = I and A a matrix so: A^t JA = J. prove that A is invertible so that AA^-1 = I
@YotamAlon if you know that the determinant obeys $\det(AB)=\det(A)\det(B)$ and that a matrix over a field is invertible iff it has nonzero determinant, you can solve this.
1d
answered be J be a matrix so: JJ^-1 = I and A a matrix so: A^t JA = J. prove that A is invertible so that AA^-1 = I
1d
comment be J be a matrix so: JJ^-1 = I and A a matrix so: A^t JA = J. prove that A is invertible so that AA^-1 = I
Indeed. Yotam, are you sure the problem is stated exactly as it was given to you?
1d
revised Simple questions about the Jacobson Radical
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1d
answered Simple questions about the Jacobson Radical
2d
answered Space time algebra isomorphic to matrix algebra
2d
comment For any group $G$, $|G/Z(G)| \neq 91$.
Yes, a Sylow $p$-subgroup is normal iff it is unique.
2d
answered For any group $G$, $|G/Z(G)| \neq 91$.
2d
revised Given two linear transformations, find the preimage of a given point for the composite transformation
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2d
revised Given two linear transformations, find the preimage of a given point for the composite transformation
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2d
answered Given two linear transformations, find the preimage of a given point for the composite transformation