# Thread: parallelogram - proof

1. ## parallelogram - proof

One of the Quadrilateral is a parallelogram and one not.
Who isn't a parallelogram and why

thanks!

2. ## Re: parallelogram - proof

Originally Posted by mentaman10

One of the Quadrilateral is a parallelogram and one not.
Who isn't a parallelogram and why
There is something very misleading about those diagrams.
It appears that one has a diagonal of length 14units and the has one of 10units. Is that really what you mean?

yes

4. ## Re: parallelogram - proof

Originally Posted by mentaman10
yes
In that case:
let $AB=\sqrt{14^2-5^2}~\&~KN=\sqrt{10^2-7^2$, both would be rectangles.
What does that tell you?

5. ## Re: parallelogram - proof

not rectangle, parallelogram.
and that doesn't give me nothing, the teacher gave me to do that..

one of them isn't and of them yes.

6. ## Re: parallelogram - proof

Originally Posted by mentaman10
not rectangle, parallelogram.
and that doesn't give me nothing, the teacher gave me to do that..
one of them isn't and of them yes.
Don't you realize that all rectangles are parallelograms?

You teacher gave you a faulty problem unless you left out some other measurement.

7. ## Re: parallelogram - proof

ofcurse I know that all the rectangle are parallelogram.
but you can't proof that it is rectangle with out proof it is parallelogram usually...
Anyway, you said both of them can be parallelogram but one of them isn't.

and we don't need to proof here that someone is a parallelogram, we need to proof that some isn't parallelogram.

8. ## Re: parallelogram - proof

The issue is that there are multiple representations of quadrilaterals, both parallelograms or not, with one pair of opposite sides being x and a diagonal being y. These constructions you have shown us make it impossible to definitely determine whether or not they're parallelograms, since there are possibilities for both depending on the values of the ambiguities. What I'm led to believe is that you or the teacher left out some angle measures or side lengths or parallel notches.