The missing piece of information in the proof is that m∠DOA and m∠BOC are vertical opposite angles.
<h3>How to find vertically opposite angles?</h3>
We want to prove that m∠BOC = 90°.
We are given that m∠AOB is a right angle triangle. Thus;
m∠BOC must also be equal to 90°
Now, since m∠BOC and m∠AOB are right angles, then it means that we must equally say that m∠DOA and m∠BOC are vertical opposite angles and they are as such equal.
Thus, the missing piece of information in the proof is that m∠DOA and m∠BOC are vertical opposite angles.
Read more about vertical opposite angles at; brainly.com/question/24425517
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