On The Absolute Value of The Product and the Sum of Linear Operators

Abstract: Let $A,B\in B(H)$. In the present paper, we establish simple and interesting facts on when we have $|A||B|=|B||A|$, $|AB|=|A||B|$, $|A\pm B|\leq |A|+|B|$, $||A|-|B||\leq |A\pm B|$ and $||A|-|B||\leq |A\pm B|$, where $|\cdot|$ denotes the absolute value (or modulus) of an operator. The results give some other interesting consequences.