urgent!! help in maths extended

[xiaotian]

please can anyone help me with the last question of paper 4, 2009 june????? i would like to know how to do question 11 part d i) and ii)
thanks =D
http://www.xtremepapers.net/CIE/index.p ... 9_qp_4.pdf

 

[PlanetMaster]

The formula is given n(n +1)/2

Using this formula for (n+1) = [(n +1)(n + 2)]/2

Sum of the nth and the (n+1)th terms:
= n(n +1)/2 + [(n +1)(n + 2)]/2
= (n+1)²

 

[ZaidOwns]

nice skills planet, you math teacher? =D

 

[PlanetMaster]

Nope!

 

[xiaotian]

thanks very much...! but can u tell me where did u get the (n+2)

 

[shalado95]

when u add 1 to the equation... u get.... n(n+1)/2 +1
Now u need a common denominator for 1 and the equation! So 1x2/1x2 u get
n(n+1)+2/2 ... if u expand u get n^2+n+1+2/2 whc basically gives u n^2+n+3/2
and when u factorize the equation n^2+n+3 (middle term split up) ...tadaaaa u get (n+2) (n+1)

heee....hope it helped!

 

[shalado95]

oh and...
P.S:
by n^2 I mean n square!