Number pattern Question... O lvl

popikachu SG · 2007-10-27T16:54:51+00:00

work backwards you are right. but how you derive at the solution ? i was thinking that the +3+5+7+9 thingy was 2n+1, but stuck there liao and wad is ap

eagle SG

if u use the summation symbol in your answer, I'm pretty sure they will not give full marks. Why should they bother to confirm it if the Cambridge answer sheet did not use the summation sign?

Another way, if you can see it, and using building on your way is

3 + SUM (2i-1) from i = 1 to i = n

SUM(-1) from i=1 to i=n = -n

SUM(2i) from i=1 to i=n = n(n+1)

so you get 3 + n^2 + n - n = 3 + n^2

AMEN567889 SG

Use APGP la.
Dont say dun know
if dun know go learn!

eagle SG

or remember this rules:

Sum (i) from i=1 to i=n = n(n+1)/2
Sum (i^2) from i=1 to i=n = n(n+1)(2n+1)/6
Sum (i^3) from i=1 to i=n = ( n(n+1)/2 )^2

if i does not start from 1, you can always make it start from 1

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