\[y = x^{2}.\]
\[x \in \lbrack 1;5\rbrack:\]
\[x = 1 \Longrightarrow y = 1^{2} = 1;\]
\[x = 5 \Longrightarrow y = 5^{2} = 25.\]
\[y \in \lbrack 1;25\rbrack.\]