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Can anyone help me. My daughter (age 9) has some maths homework that I can't help her with as I don't understand it. She has to work out the diagonals in various polygons. (I didn't even know what a polygon was until tonight). Can anyone point me in the right direction?

Could you scan a picture over here (my son had to work out the diagonals in various polygons last year, he's nine now - at the moment they have multiplication, with numbers between 0 to 999, one below the other with equations that has substractions or addition in them and verbal exercises )

I would Mari but as well as being rubbish at maths I am also rubbish at computer stuff and wouldn't know how to. I can tell you that the first shape is just a rectangle and my daughter has worked out that there are 25 diagonals in it. Does that Help? I just wanted to know if she was on the right track and had hoped I could find a website but they are all a bit advanced. (for me anyway)

All I can tell you is 90 degrees in a right angle,so if it's sliced in half will be 45 degrees.
I can't think what it might be,tho.Don't recall any of mine being set anything like that,sorry

Being that she's only 9 Im guessing that she doesnt have to use any kind of mathematical equation to get to the answer therefore I would say a rectangle has 2 diagonals (ie if you sliced it in half diagonally from corner to corner).

Ive attached a (VERY BASIC) picture showing what I mean so in other words A-D = 1 diagonal and B-C = 1 Diagonal making 2.

Of course I could be totally wrong but at 9 years old I seriously cant think it would be any more complicated!

found some more polygons here

also this quote

Thanks Obo. She has managed to find 25 on her rectangle

After my inital thoughts I did some searching online and I would bet at least a tenner that there's only 2 Ellie

I could be wrong (though 25 sounds very high)

Thanks Obo. I agree with you but think I will leave it to her teacher to explain it, as I'm a bit dim on these things.

Yep it could be Ive totally missed the mark (not difficult for me) I hope she does ok with it

Im off to bed now

Sounds way to complex for Yr5,Ellie.I'd suggest that in a rectangle at this stage they'd only bisect....i.e. the angles are 45 degrees??

Yes, two must be the correct answer. In the link that Obo gave, it gave a formula to work out the result:-



n multiplied by (n-3) and then divided by 2 = diagonals (where n = number of sides of polygon)

Therefore, for a rectangle (4 sides) the number of diagonals =

4 multiplied by (4-3) divided by 2 which equals 4 X 1 divided by 2 which equals 4 divided by 2 = 2

The link which Obo gave is actually very good at explaining it all and may be worth showing your daughter. Obo explained it very well as well.

Thanks guys. It turned out that she got it completely wrong. The rectangle had dots at several points and she thought she had to draw the polygons from various points where the dots where. Of course I was no help and she got every single one of them wrong. But on a good note, she now understands it entirely and when I showed her the link, she knew exactly what it meant, which is more than I can say.

At least she learnt something from it thats the main thing