I'm reading "Noncommutative Rings" by Herstein, and I got stuck in theorem 1.2.5/page 16. It says: "if $A$ is an two -sided ideal of a noncommutive ring $R$ (may be not unity) then $J(A)=A \cap J(R)$."
Jacobson radical of a ring $R$ is the intersection of all maximal regular right ideal of $R$.
Anyone could explain the theorem?