1/
$\Delta$ ABC ~ $\Delta$ MNP
=> $\frac{AB}{MN}= \frac{BC}{NP}= \frac{AC}{MP}= \frac{2}{3}$
=> $\frac{3}{MN}= \frac{4}{NP}= \frac{AC}{MP}= \frac{2}{3}$
=> MN= 4,5cm; NP= 6cm
$C_{MNP}= MN+ NP+ MP= 19,5cm$
=> MP= 9cm
=> AC= 6cm
2/
$\Delta$ ABC ~ $\Delta$ B'A'C'
=> $\widehat{A}= \widehat{B'}$; $\widehat{B}= \widehat{A'}$; $\widehat{C}= \widehat{C'}$
$\frac{AB}{B'A'}= \frac{AC}{B'C'}= \frac{BC}{A'C'}$
3/
$\Delta$ ABC ~ $\Delta$ MNQ
$\Delta$ MNQ ~ $\Delta$ FDE
=> $\Delta$ ABC ~ $\Delta$ FDE
=> A sai, B đúng, C sai, D đúng
