Let $A$ be a $C^*$-algebra. How to prove that $\|1-\frac{x}{\|x\|}\|\leq 1$ implies positivity of $x$? The converse can be shown to be true using functional calculus.
2026-03-28 00:25:40.1774657540
An equivalent condition for positivity
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Consider the complex plane and take a point on the unit circle close to $1$. This satisfies your hypothesis but the point need not be positive.