角BAC=角AOD-角ABD=(180-角DAC)-角ADB-角ABD
=角ADC+角ACD-(90-1/2角BDC)-(角ABD)
=90+1/2角BDC+角ACD-(90-1/2角BDC)-角ACD
=角BCD
于是证明了三角形ABC是等腰三角形.
角BAC=角AOD-角ABD=(180-角DAC)-角ADB-角ABD
=角ADC+角ACD-(90-1/2角BDC)-(角ABD)
=90+1/2角BDC+角ACD-(90-1/2角BDC)-角ACD
=角BCD
于是证明了三角形ABC是等腰三角形.