Bài 1:
a) Hình vẽ
b) Ảnh thật, ngược chiều, lớn hơn vật
c) Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{{20}}{{OA'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' - OF'}} = \dfrac{{12}}{{OA' - 12}}\\
\Rightarrow \dfrac{{20}}{{OA'}} = \dfrac{{12}}{{OA' - 12}} \Rightarrow OA' = 30cm\\
\Rightarrow \dfrac{{AB}}{{A'B'}} = \dfrac{2}{3} \Rightarrow A'B' = 9cm
\end{array}\)
Bài 6:
a) Hình vẽ
b) Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{{15}}{{OA'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF}}{{ - OA' + OF}} = \dfrac{{10}}{{10 - OA'}}\\
\Rightarrow \dfrac{{15}}{{OA'}} = \dfrac{{10}}{{10 - OA'}} \Rightarrow OA' = 6cm\\
\Rightarrow AB = 0,8cm
\end{array}\)