Qualification > Math

IGCSE MATHS Doubts

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mdwael:
1,2,4,7,11,16 whats the nth term for this kindof sequence? gradually adding by increasing numbers +1 +2 +3 but how do you find the nth term?

CatAly$t:

--- Quote from: ~VIN1094~ on May 18, 2010, 07:19:52 pm ---all taken from the forum ..

--- End quote ---

thanks!!!u saved my life.... :D

Ghost Of Highbury:

--- Quote from: mdwael on May 18, 2010, 08:22:25 pm ---1,2,4,7,11,16 whats the nth term for this kindof sequence? gradually adding by increasing numbers +1 +2 +3 but how do you find the nth term?

--- End quote ---

'Changing Difference' Sequences

The general term for term number 'n' , common diff. 'd' , first term 'a' and difference change 'c'is:

a+d(n-1)+c/2(n-1)(n-2)

a = 1
d = 1 (first difference)

1  2  4  7   11
  1  2  3   4

    1  1  1

c = 1 (final difference)

a+d(n-1)+c/2(n-1)(n-2)

1+(n-1)+0.5(n-1)(n-2)

1+n-1+0.5(n^2 -3n + 2)

1+n-1+0.5n^2 - 1.5n + 1

0.5n^2 -0.5n + 1.

M'i'D'o:
Can anybody plz solve the question 9 in nov 06 paper 4 and attach it for me...
Inequalities... I HATE IT.. plzz heeelp i'm dying for it......

Shazizzzle:
Keeping up with everything here is so hard! :P At times, there are like 7 replies once you click submit.

Anyway, I'm having an offline revision today, so later guys.

And BEST OF LUCK! :D

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