if (((m∠ABC) + (m∠BCA)) + (m∠CAB)) + (((m∠ACD) + (m∠CDA)) + (m∠DAC)) = (((((m∠ABC) + (m∠BCA)) + (m∠CAB)) + (m∠ACD)) + (m∠CDA)) + (m∠DAC), then (((m∠ABC) + (m∠BCA)) + (m∠CAB)) + (((m∠ACD) + (m∠CDA)) + (m∠DAC)) = (((m∠ABC) + (m∠CDA)) + ((m∠BCA) + (m∠ACD))) + ((m∠DAC) + (m∠CAB))

Start from the conclusion and work back up the proof. Click the arrow to show the parents.