Let $K$ be an algebraically closed field extension of $F$. Show that the algebraic closure of $F$ in $K$ is an algebraic closure of $F$.

Question

Let $K$ be an algebraically closed field extension of $F$. Show that the algebraic closure of $F$ in $K$ is an algebraic closure of $F$.

I have been thinking a lot about this problem but I do not quite understand what it is that asks me the problem, this result is not obvious? What to try? I appreciate any explanation, thank you very much.