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 November 5th, 2014, 06:59 AM #1 Newbie   Joined: Mar 2012 Posts: 4 Thanks: 0 Algebraic Sequence. CIE past paper. Can't Solve :'( How can question (iii) be solved (a) The nth term of a sequence is n(n+1). (i) Write the two missing terms in the spaces. 2, 6, , 20, [2] (ii) Write down an expression in terms of n for the (n + 1)th term. Answer(a)(ii) [1] (iii) The difference between the nth term and the (n + 1)th term is pn + q. Find the values of p and q.
November 5th, 2014, 07:37 AM   #2
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 Originally Posted by Kumail How can question (iii) be solved (a) The nth term of a sequence is n(n+1). (i) Write the two missing terms in the spaces. 2, 6, , 20, [2] (ii) Write down an expression in terms of n for the (n + 1)th term. Answer(a)(ii) [1] (iii) The difference between the nth term and the (n + 1)th term is pn + q. Find the values of p and q.
(i) 1(1+1) = 2, 2(2+1) = 6, 3(3+1) = ? , 4(4+1) = 20, ...

(ii) $\displaystyle a_n = n(n+1)$ ... to find $\displaystyle a_{n+1}$, substitute $\displaystyle (n+1)$ in for $\displaystyle n$ in the nth term

(iii) once you determine the (n+1)st term, do the subtraction

 November 5th, 2014, 05:53 PM #3 Newbie   Joined: Mar 2012 Posts: 4 Thanks: 0 I was able to solve first and second question without any trouble. I was also able to determine the (n+1)th term. But in 3, I was not able to form the simultaneous equation!
 November 5th, 2014, 08:38 PM #4 Global Moderator   Joined: Dec 2006 Posts: 19,049 Thanks: 1618 {iii) As (n + 1)((n + 1) + 1) - n(n + 1) = 2(n + 1) = 2n + 2, p = q = 2. Thanks from Kumail

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# write down an algebraic expression for the (n-1)th term of the sequence

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