2
$\begingroup$

Exercise 3, page 13 from Golan's book ("The Linear Algebra a Beginning Graduate Student Ought to Know"): Define a new operation $\circ$ on $\mathbb{R}$ by setting $a\circ b= a^{3}b.$ Show that $\mathbb{R}$, on which we have the usual addition and this new operation as multiplication, satisfies all of the axioms of a field with the exception of one.

My work: The new operation is not commutative and there is no identity of multiplication. If there exists $x\in \mathbb{R}$ such that $a\circ x= a = x\circ a$, then $a^{3}x=a=x^{3}a$. If $a\neq 0$ then $x=1$ and the first equality would gives us $a=\pm 1$.

Is the exercise wrong or I am doing something wrong?

Thanks in advance!

PS.Please, correct any mistake I made.

  • 0
    Note that the axio$m$ on page 6 does not requ$i$re the identity to be 2-sided. But it does require a right identity, and that doesn't hold here either. So you may have had a minor technical oversight, but you're still correct that there is more than one property missing.2012-01-25

0 Answers 0