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 \(k = \dfrac{1}{2}\)

\(\widehat B = \widehat {\dfrac{A}{3}}\)

\(\widehat B = \dfrac{2}{3}\widehat A\)     

\(\widehat B = \widehat {\dfrac{A}{2}}\)

\(\widehat B = \widehat C\)