Question 181206
Identify the conjecture to be proven.
Given: ABC is an obtuse , 
B is an obtuse angle;
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Prove: ABC does not have a right angle.
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2. Assume the opposite of the conclusion. Write this assumption.Assume ABC does have a right angle. Let A be a right angle.
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3. Use direct reasoning to arrive at a contradiction. Possible answer: If A is a right angle, then measurement of angle B + angle C =90°. But angle B is  > 90°, since B is obtuse. So this is a contradiction.
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4. What can you conclude? The assumption that ABC does have a right angle is false. Therefore ABC does not have a right angle. .