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# May you please explain this simple Geometry concept?

I'm working on finding the nth term in patterns in crap but I am having trouble explain this one.

1, 3, 6, 10, 15, 21

I know it's changing by 2 but with a difference of +1 each tern, but I don't know how to label it!

Also, I don't understand when it asks, "If a polyagnial has 100 sides, how many diagonals may it have?"

Please explain these two, this is the second time I've failed this Geometry test. Grr.

### 2 Answers

- 9 years ago
Nope you don't know . look at it again. 1+(1+1) 3+(2+1) 6+(3+1) 10+(4+1)

Second one Draw even sided shapes 4 6 8 10 ..... Find the pattern then you'll find your equation then you can find the number of diagonals for 100.

Have fun... I could do these for you but what would you learn?

- Anonymous9 years ago
If nth term is Xn then

Xn=X(n-1)+(X(n-1)-X(n-2)+1)

For the second quenstion i have to refer something

No of diagonals of any polygonal having n number of sides is

(n^2-3n)/2

Source(s): http://en.wikipedia.org/wiki/Diagonal