Câu 1:
Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = 1\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' - OF'}} = \dfrac{{30}}{{OA' - 30}}\\
\Rightarrow 1 = \dfrac{{30}}{{OA' - 30}} \Rightarrow OA' = 60cm
\end{array}\)
Câu 2:
Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{{28}}{{OA'}} = 2 \Rightarrow OA' = 14cm\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' - OF'}} = \dfrac{f}{{14 - f}}\\
\Rightarrow 2 = \dfrac{f}{{14 - f}} \Rightarrow f = \dfrac{{28}}{3}cm
\end{array}\)