Question

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

Theorem: In a quadrilateral, there cannot be more than three obtuse angles.

Heather begins the proof with an assumption. Which statement will she most likely use as an assumption?

Let one angle of a quadrilateral be acute and the other three angles obtuse.

Let all angles of a quadrilateral be obtuse.

Let only one angle of a quadrilateral be obtuse.

Let one angle of a quadrilateral be obtuse and the other three angles acute.

Answer 1

@ganeshie8

Answer 2

@Mertsj @ranga @sourwing

Answer 3

A proof by contradiction begins by assuming the opposite of what you want to prove.
Your theorem says to prove that in a quadrilateral there are at most 3 obtuse angles.
So you should assume that there are 4 obtuse angles.