Given a function $f~:~X\to Y$ and a set $A\subseteq X$, we wish to prove the following:
$$A\subseteq f^{-1}(f(A))$$
My attempt:
Let $x\in A$. This implies $\exists y\in Y$ such that $f(x)=y$
Then $f^{-1}(f(x))=f^{-1}(y)=x$. Is this right?
Given a function $f~:~X\to Y$ and a set $A\subseteq X$, we wish to prove the following:
$$A\subseteq f^{-1}(f(A))$$
My attempt:
Let $x\in A$. This implies $\exists y\in Y$ such that $f(x)=y$
Then $f^{-1}(f(x))=f^{-1}(y)=x$. Is this right?
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If $a \in A$, then $f(a) \in f(A)$. Thus $ a \in f^{-1}(f(A))$.