On the invertibility of AA+−A+A in a Hilbert space

Abstract

Let $H$ be a Hilbert space and $B(H)$ the algebra of all bounded linear operators on $H$. In this paper, we study the class of operators$AınB(H)$ with closed range such that $A{A}^{+}-A^{+}A$ is invertible, where $A^{+}$ is the Moore-Penrose inverse of $A$. Also, we present new relationsbetween $(A{A}^{\ast }+A^{\ast }A{)}^{-1}$ and $(A+A^{\ast }{)}^{-1}$. The present paper is an extension of results from[J. Ben\ítez and V. Rakočević, Appl. Math. Comput. 217 (2010) 3493–3503] to infinite-dimensional Hilbert space.