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MATH HELP? It's a toughy.

whuk

Shameless Fairy

12,375 Points

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Posted: Sat Jun 13, 2009 6:26 pm

Okay, so here is the puzzle. I need to connect two number sets. (It's not homework, just the end result of something fun I did.)

x - y
1 - 0
2 - 2
3 - 8
4 - 20
5 - 40
6 - 70
7 - 112
8 - 168
9 - 240

Make an equation for the information above.

sample

Here is a sample number set.

x - y
1 - 2
2 - 4
3 - 6
4 - 8
5 - 10

The equation or formula or whatever in this case is 2x = y.

Posted: Wed Jul 15, 2009 11:30 pm

If you half it and you're familiar with binomial coefficients, this becomes obvious: y = 2C(x+1,3) = (x³-x)/3.

VorpalNeko

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slayerlx
Crew

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Posted: Sat Oct 03, 2009 7:15 pm

y={0, x=1, 2, x=2, 8, x=3, 20, x=4, 40, x=5, 70, x=6, 112, x=7, 168, x=8, 240, x=9}

Piecewise'd

but seriously, it's only y=sum n(n-1),n=1 to x , or in calculator form, it's sum(seq(n(n-1),n,1,x))

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