Question

Write an indirect proof proving only one angle of an obtuse triangle is greater than 90°. (11 points)

Answer 1

the top angle of the obtuse triangle is bigger than 90. proof, if it isn't, then it would be either a right triangle or an acute triangle

Answer 2

but that isnt a proof @hashbasl

Answer 3

then i don't have any hard evidence. try answers.yahoo.com

Answer 4

To do an indirect proof, assume the negation of what you want to prove. Then, show that the assumption leads to a contradiction.

Answer 5

so one angle is greater than 90

Answer 6

Prove Indirectly that an obtuse triangle ABC has exactly one obtuse angle.
Proof:
Temporarily assume that a given obtuse triangle ABC has two obtuse angles, <A and <B.
An obtuse angle has measure greater than 90.
The sum of the interior angles of a triangle is equal to 180.
In triangle ABC, m<A + m<B + m<C = 180.
But, m<A > 90 and m<B > 90.
In the equation, m<A + m<B + m<C would be greater than 180 because two of the angles are greater than 90. Greater than 90 plus greater than 90 + m<C is in excess of 180 which cannot be.
This contradicts the assumption that Triangle ABC has two obtuse angles.
The assumption, then, is false.
Therefore, the obtuse triangle has exactly one obtuse angle.