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

You are not logged in.

#1 2013-03-08 12:55:17

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

Sequence question

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

#2 2013-03-08 13:16:56

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 81,467

Re: Sequence question

Hi;

You can use differences to get the answer


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Online

#3 2013-03-08 15:23:30

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

Re: Sequence question

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

Board footer

Powered by FluxBB