#### cecilia_p

##### New member
if the sides in a parallelogram are 3 cm and 5 cm can the diagonal in the parallelogram be 10 cm? 8 cm? 4 cm? why?

D

#### Deleted member 4993

##### Guest
if the sides in a parallelogram are 3 cm and 5 cm can the diagonal in the parallelogram be 10 cm? 8 cm? 4 cm? why?
Think about "sides of a triangle". What is possible and not possible there?

#### topsquark

##### Senior Member
if the sides in a parallelogram are 3 cm and 5 cm can the diagonal in the parallelogram be 10 cm? 8 cm? 4 cm? why?
Make a sketch. Can you have a triangle with a sides 3 cm and 5 cm with a diagonal of 10 cm? What would the triangle have to look like?

-Dan

#### The Highlander

##### Full Member
if the sides in a parallelogram are 3 cm and 5 cm can the diagonal in the parallelogram be 10 cm? 8 cm? 4 cm? why?
Do you know as well as understand the triangle inequality?

Imagine for yourself (in your mind's eye) what happens to the length of side c as the vertex C moves up and down.

Last edited by a moderator:

#### Harry_the_cat

##### Elite Member
Forget all the theory. Get out a pen and a ruler and try to draw them!

#### The Highlander

##### Full Member
Forget all the theory. Get out a pen and a ruler and try to draw them!
Why would s/he need to draw anything when the answer is obvious from the final (red) line in post #5?

#### Harry_the_cat

##### Elite Member
It's obvious for us, but I think you get a better feel for it, and are therefore more likely to remember it, if you put pen to paper. Call me old-fashioned!!

#### pka

##### Elite Member
It's obvious for us, but I think you get a better feel for it, and are therefore more likely to remember it, if you put pen to paper. Call me old-fashioned!!
It could be the case that no pen and ruler are allowed, think an ACT type test.
The question is clearly testing the concept of the triangle inequality.

#### The Highlander

##### Full Member
It's obvious for us, but I think you get a better feel for it, and are therefore more likely to remember it, if you put pen to paper. Call me old-fashioned!!
You're Old-Fashioned.