Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**infinitebrain****Member**- Registered: 2008-07-01
- Posts: 153

Given the sequence

find k

I found the answer as 291, through a tedious guess and check method, but I'd like someone to explain in simpler terms how to find k.

*Last edited by infinitebrain (2013-03-08 12:55:30)*

The best thing about life is you don't know what to expect

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,376

Hi;

You can use differences to get the answer

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

Offline

**Stormtangent****Member**- Registered: 2011-09-03
- Posts: 33

Hi,

If you subtract consecutive terms, you see that you get:

Subtracting again, you get

You could find the quadratic. However, another way is to realize that

, which, after solving, gives*Last edited by Stormtangent (2013-03-08 15:25:26)*

"Have you ever had a dream that you were so sure was real? What if you were unable to wake from that dream? How would you know the difference between the dream world and the real world? "

Offline

Pages: **1**