Abstract Algebra: Commutative Subgroup

[pat bismark]

Homework Statement

Let G be a group and let a, b be two fixed elements which commute with each other (ab = ba). Let H = {x in G | axb = bxa}. Prove that H is a subgroup of G.

Homework Equations

None

The Attempt at a Solution

I'm using the subgroup test. I know how to show that the identity of G exists in H and that if x1, x2 exist in H then x1 times x2 exists in H but need help proving that if x is in H then x^-1 is also in H. I've tried starting with axb = bxa and multiplying on the right and left with various combinations of a, x^-1, and b, but can't get it to the form ax^-1b = bx^-1a.

Please let me know if you have any ideas, thanks.

 

[phsopher]

Prove that [b^-1,a] = [b,a^-1] = 0 and use that along with the fact that axb = bxa.