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This question concerns the group of matrices

L = { (a 0)

(c d) : a,c,d ∈ R, ad =/ 0}

under matrix multiplication, and its subgroups

H = { (p 0, (p - q) q) : p,q ∈ R, pq =/ 0} and K = { (1 0, r 1) : r ∈ R}

Show that one of H and K is a normal subgroup of L and that the other is not.

Any pointers would be fantastic!! Struggling and is from a previous assignment but just can't seem to figure this out?!

I understand that klk^-1 gives a lower triangular matric similar to L. Which would be this is a subgroup of L

But when i multiply together lhl-1 is seem to also get a lower traingular matrix?

Any pointer to where i am going wrong?