Given: m∠ADB not equal m∠BDC Prove: -->(ray) DB  is not the bisector of ∠ADC

 
                                        ->
1.  Assume, for contradiction, that ray DB is the bisector of ∠ADC
2.  m∠ADB = m∠CDB  (definition of angle bisector)
3.  Contradiction to what we are given:  m∠ADB not equal m∠BDC 

Edwin
PS.  Do not use < for ∠ because the computer thinks it is the beginning
of an HTML tag and deletes what comes after it. The code for the angle symbol
∠ is & #8736; without the space between the & and the #.