\(\Delta OA'B'\sim\Delta OAB\\ \Rightarrow\frac{A'B'}{AB}=\frac{OA'}{OA}\)
\(\Delta A'B'F'\sim\Delta OIF'\\ \Rightarrow\frac{A'B'}{OI}=\frac{A'F'}{OF'}\)
mà AB = OI , OF = OF' , A'F' = OA' - OF'
\(\Rightarrow\frac{OA'}{OA}=\frac{OA'-OF}{OF}\\ \Rightarrow\frac{OA'}{24}=\frac{OA'-12}{12}\\ \Rightarrow12.OA'=24\left(OA'-12\right)\\ \Leftrightarrow12.OA'=288\\ \Rightarrow OA'=24\left(cm\right)\)
\(\frac{A'B'}{AB}=\frac{OA'}{OA}\Rightarrow\frac{A'B'}{1}=\frac{24}{24}\Rightarrow A'B'=1\left(cm\right)\)
(sai thì thôi nhia ~~~~~)