Since DB and AF are congruent diagonals of ADFB which bisect the base angles DAB and FBA,
ADFB must be an isoceles trapezoid.
Raya wrote:From the information given, we know that ADFB has congruent diagonals which bisect the lower base angles. I have taken this to prove that ADFB is an isoceles trapezoid
threewood14 wrote:We know that the two diagonals are congruent.
threewood14 wrote:Here is what I am working on.
Look at triangles ACF and BCD. If we can prove that these triangles are congruent, then we prove that triangle ABC is isosceles!
triangles with two congruent sides must themselves be congruent
threewood14 wrote:triangles with two congruent sides must themselves be congruent
I do not think that triangles with two common sides must themselves be congruent. You also need an angle or another side.
Jung He Fah Toy wrote:If either of the triangles Lex and threewood were pointing out can be proven congruent, then the problem can be solved!
threewood14 wrote:I'm glad you found that, but we are trying to prove it with a geometric proof...Sorry
Besides, reductio ad absurdum is a valid mathematical way of proving something.each [allegedly direct proof] is really an indirect proof in disguise.
C
/ / \
b / /t \ a
/ / \
A----P----------B
m n
threewood14 wrote:I think the challenge is using the Law of Sines...
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