Hãy chọn câu đúng. Nếu $\Delta ABC$ và $\Delta DEF$ có $\widehat B = \widehat {D;}\,\dfrac{{BA}}{{BC}} = \dfrac{{DE}}{{DF}}$ thì:

$x = 3\,$         

$x = \dfrac{{27}}{7}$

$x = 4\,$         

$x = \dfrac{{27}}{5}$ 

$12\,cm$

$6\,cm$

$10\,cm$

$8\,cm$

$\Delta ABC\backsim\Delta DEF$

$\Delta CAB\backsim\Delta DEF$

$\Delta ABC\backsim\Delta DFE$

$\Delta CBA\backsim\Delta DFE$

$\Delta \;ADE\backsim\Delta \;ABC$       

$DE{\rm{//}}BC$     

$\dfrac{{AE}}{{AB}} = \dfrac{{AD}}{{AC}}$       

$\widehat {ADE} = \widehat {ABC}$

$\Delta A'B'C'$$\backsim$$\Delta ABC$ theo tỉ số $k = \dfrac{1}{2}$            

$\Delta EDF$$\backsim$$\Delta ABC$ theo tỉ số $k = \dfrac{1}{2}$  

$\Delta A'B'C'$$\backsim$$\Delta ABC$ theo tỉ số $k = \dfrac{1}{4}$           

$\Delta A'B'C'$$\backsim$$\Delta EDF$ theo tỉ số $k = \dfrac{1}{2}$

$\widehat B = \widehat {\dfrac{A}{3}}$

$\widehat B = \dfrac{2}{3}\widehat A$     

$\widehat B = \widehat {\dfrac{A}{2}}$

$\widehat B = \widehat C$