The only way for a quadrilateral to have equal diagonals is

[Vik]

I was doing one Manhattan Archive question square peg and roung hole ( Dated 12.2003) . In the solution it has been mentioned
"The only way for a quadrilateral to have equal diagonals is if its corners are 90 degrees"
Intutively I can say that evenif diagonals of quadrilateral are equal , It can be possible that corners are not 90 degree

Please explain.

I can post Manhattan Archive full question if needed ... "Jeff is painting two murals on the front of an old apartment building that he is renovating. One mural will cover the quadrilateral face ....."

[Aragorn]

I think you are using CR techniques here. May be powerscore book?

Anyways...
If A then B (is given)
it implies if not B then not A

However...it is given that iff A then B
that means, it is given that if A then B and if not A then not B

So we can conclude...
iff not B then not A

iff= if and only if

[rfernandez]

Vik, you're right... an isosceles trapezoid is an example of a quadrilateral with diagonals of equal length but whose "corners" need not be 90 degree angles. I will request that the solution be changed accordingly.

Despite this, the correct answer to the problem is unchanged: C.

Rey