Vì AB=AD, $\widehat{ABC} = \widehat{ADC} = 90^{0}$
=> $\Delta ABD = \Delta ABC$ (cạnh huyền-cạnh góc vuông)
=> $\widehat{ACB} = \widehat{ACD}$
Vì AB=AD, $\widehat{ABC} = \widehat{ADC} = 90^{0}$
=> $\Delta ABD = \Delta ABC$ (cạnh huyền-cạnh góc vuông)
=> $\widehat{ACB} = \widehat{ACD}$