Đáp án:
1. Ảnh thật, ngược chiều, lớn hơn vật
Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{{24}}{{OA'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' - OF'}} = \dfrac{{18}}{{OA' - 18}}\\
\Rightarrow \dfrac{{24}}{{OA'}} = \dfrac{{18}}{{OA' - 18}} \Rightarrow OA' = 72cm\\
\Rightarrow \dfrac{{AB}}{{A'B'}} = \dfrac{1}{3} \Rightarrow A'B' = 4,5cm
\end{array}\)
2. Ảnh ảo, cùng chiều, lớn hơn vật.
Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{{12}}{{OA'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' + OF'}} = \dfrac{{18}}{{OA' + 18}}\\
\Rightarrow \dfrac{{12}}{{OA'}} = \dfrac{{18}}{{OA' + 18}} \Rightarrow OA' = 36cm\\
\Rightarrow A'B' = 4,5cm
\end{array}\)
