Preimage of Subset under Mapping/Examples/Subset of Image of Square Root Function

Example of Preimage of Subset under Mapping

Let $f: \R \to \R$ be the real function defined as:

$\forall x \in \R: \map f x = x^2$

Let $A \subseteq \R$ be defined as:

$A := \closedint 4 9 = \set {x \in \R: 4 \le x \le 9}$

Then the preimage of $A$ under $f$ is:

$f^{-1} \sqbrk A = \closedint {-3} {-2} \cup \closedint 2 3$

Let $B \subseteq \R$ be defined as:

$B := \closedint {-9} {-4} = \set {x \in \R: -9 \le x \le -4}$

Then the preimage of $B$ under $f$ is:

$f^{-1} \sqbrk B = \O$

Sources

• 1967: George McCarty: Topology: An Introduction with Application to Topological Groups ... (previous) ... (next): Chapter $\text{I}$: Sets and Functions: Functions