# What is the radical of upper triangular matrices?

Let $$B$$ be the algebraic group of upper triangular matrices with entires in some algebraically closed field. I would like to know what is the radical of this group is... Any explanation would be appreciated. thanks you.

The unipotent radical of the group $$B_n(K)$$, which is the standard Borel subgroup of $$GL_n(K)$$, consists of unitriangular uppertriagular matrices, i.e., with all diagonal elements equal to $$1$$. The (solvable) radical of $$B_n(K)$$ equals $$B_n(K)$$ itself, since the Borel subgroup is solvable.