\(\Delta ABO\infty\Delta A'B'O\Rightarrow\dfrac{AB}{A'B'}=\dfrac{OA}{OA'}\left(1\right)\)
\(\Delta OFI\infty\Delta A'FB'\Rightarrow\dfrac{OF}{A'F}=\dfrac{OI}{A'B'}\)
\(\Rightarrow\dfrac{OF}{OF-OA'}=\dfrac{AB}{A'B'}\left(2\right)\)
(1,2) \(\Rightarrow\dfrac{OF}{OF-OA'}=\dfrac{OA}{OA'}\Rightarrow OA'=3,6cm\)
(1) \(\Rightarrow\dfrac{1,5}{A'B'}=\dfrac{9}{3,6}\Rightarrow A'B'=0,6cm\)