What's the equation that describes this number sequence:

N | D
3 | 0
4 | 2
5 | 5
6 | 9


I see the pattern, from 3 to 4, it grows by 2, then by 3, 4, etc.

N=the number of sides, and D=the number of diagnals. If you draw a triangle (three sides, so N=3), you have 0 diagnals you can draw from point to point (so D=0), which is why where N=3, D=0. Then, with a square, you have 2 diagnals, pentagon has 5 diagnals, hexagon has 9. Following the patter, N=7 would produce D=14. I drew a heptagon (7 sides), and it did have 14 diagnals. So going by the pattern, where N=8, D=20; N=9, D=27; and N=10, D=35.

Can anyone help me out on this?

Originally posted by cougar694u
What's the equation that describes this number sequence: N | D 3 | 0 4 | 2 5 | 5 6 | 9 I see the pattern, from 3 to 4, it grows by 2, then by 3, 4, etc. N=the number of sides, and D=the number of diagnals. If you draw a triangle (three sides, so N=3), you have 0 diagnals you can draw from point to point (so D=0), which is why where N=3, D=0. Then, with a square, you have 2 diagnals, pentagon has 5 diagnals, hexagon has 9. Following the patter, N=7 would produce D=14. I drew a heptagon (7 sides), and it did have 14 diagnals. So going by the pattern, where N=8, D=20; N=9, D=27; and N=10, D=35. Can anyone help me out on this?

Doh. Change majors? :thumbsup

You should really wait a day or 2 before posting this kind of stuff. I'm sure that I'm not the only one who is still recuperating from last night...

Originally posted by eclipzGST
You should really wait a day or 2 before posting this kind of stuff. I'm sure that I'm not the only one who is still recuperating from last night...

Which is why my brain is not functioning and I can't figure it out.

D = < N (N - 3) > /2

Edit: The <> are brackets. It wouldn't lemme do them for some reason.

Originally posted by dsmmyth
D = < N (N - 3) > /2 Edit: The <> are brackets. It wouldn't lemme do them for some reason.

Any way to show the work. I'm impressed.

Originally posted by greygoose

Originally posted by dsmmyth D = < N (N - 3) > /2 Edit: The <> are brackets. It wouldn't lemme do them for some reason.

Any way to show the work. I'm impressed.

Lol, I actually googled that because I was too lazy to figure it out myself (College mode hasn't kicked in yet).

When it comes to formulas, I usually just plug in random crap until I get the right one.

Originally posted by dsmmyth
D = < N (N - 3) > /2 Edit: The <> are brackets. It wouldn't lemme do them for some reason.

Thanks! I had gotten partially there, but I was working on a motorcycle and gas fumes had gotten to me (I don't have any other excuses :shrug), but it seems so simple.