# parallelogram - proof

• December 8th 2011, 07:29 AM
mentaman10
parallelogram - proof
http://img443.imageshack.us/img443/2...265485tkvf.png
One of the Quadrilateral is a parallelogram and one not.
Who isn't a parallelogram and why

thanks!
• December 8th 2011, 08:01 AM
Plato
Re: parallelogram - proof
Quote:

Originally Posted by mentaman10
http://img443.imageshack.us/img443/2...265485tkvf.png
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?
• December 8th 2011, 08:07 AM
mentaman10
Re: parallelogram - proof
yes
• December 8th 2011, 08:17 AM
Plato
Re: parallelogram - proof
Quote:

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?
• December 8th 2011, 08:26 AM
mentaman10
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.
• December 8th 2011, 08:41 AM
Plato
Re: parallelogram - proof
Quote:

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.
• December 8th 2011, 09:23 AM
mentaman10
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.
• December 10th 2011, 07:57 PM
Feryll
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.