Question

In a geometry class, the students were asked to prove the theorem below by contradiction.

Theorem: In a triangle, there cannot be more than one right angle.

Heather begins the proof with an assumption. Which statement will she most likely use as an assumption?
Answer
Let each angle of a triangle be less than 90°.
Let each angle of a triangle be greater than 90°.
Let two angles of a triangle be 90°.
Let only one angle of a triangle be 90°.

Answer 1

Let two angles of a triangle be 90°.
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This is an indirect proof also known as proof by contradiction.
Begin by assuming the negation of what is to be proved. The negation of "not more than one" in this case is "two."