Artificial intelligent assistant

Uncertainty When Multiplying by $\pi$ When multiplying a number with an uncertainty by $\pi$, does the certainty differ, and if so, how? Example: $a = 10$ $\delta a = 1$ What is the uncertainty of $b$ where $b=\pi a$?

$$b = \pi(a)\;\; \implies\;\; b \;= \;10\pi\pm 1\cdot \pi \;= \;10\pi \pm \pi$$

$$\implies\;\; \delta b \;\;= \;\;\pi \;\;= \;\;\pi(\delta a)$$

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