Cho tam giác $ABC$  có $AB < AC$ . Gọi \(E \in AC\) sao cho \(AB = CE\). Gọi $O$  là một điểm nằm ở trong tam giác sao cho $OA = OC,OB = OE.$ Khi đó:

\({60^ \circ }\)

\({70^ \circ }\)

\({90^ \circ }\)           

\({120^ \circ }\)

\(\Delta BAD = \Delta HIK\)           

\(\Delta ABD = \Delta KHI\)

\(\Delta DAB = \Delta HIK\)           

\(\Delta ABD = \Delta KIH\)

\(\Delta BAD = \Delta HIK\)           

\(\Delta ABD = \Delta KHI\)

\(\Delta DAB = \Delta HIK\)           

\(\Delta ABD = \Delta KIH\)

\(\widehat {CAC'} > \widehat {CBC'}\)

\(\widehat {CAC'} < \widehat {CBC'}\)     

\(\widehat {CAC'} = \widehat {CBC'}\)     

\(\widehat {CAC'} = 2.\widehat {CBC'}\)

\(\widehat {BCA} = \widehat {BAC'}\)

\(\Delta ACB = \Delta BAC'\)

\(\widehat {BCA} = \widehat {ABC'}\)       

\(\Delta ACB = \Delta BC'A\)

\(\widehat {BCA} = \widehat {BAC'}\)

\(\Delta ACB = \Delta BAC'\)

\(\widehat {BCA} = \widehat {ABC'}\)       

\(\Delta ACB = \Delta BC'A\)

\(\Delta ABC = \Delta ACD\) 

\(\Delta ABC = \Delta CDA\)   

\(\Delta ABC = \Delta ADC\) 

\(\Delta ABC = \Delta CAD\)