Year 12s: what will be the first way you research your future options? >>

Series

ckfeister

I'm stuck on b)

Workouts down below and answer is 286, whats the mistakes I'm doing?

(edited 7 years ago)

Reply 1

ckfeister

Edited and got the question on there, can't remove the long stupid coding stuff though, its not on edit mode.

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Reply 2

Pangol

It looks like you are using the wrong expression for the sum of the integers (you've used the expression for the sum of the squares of the integers again).

Reply 3

NotNotBatman

Original post by ckfeister

Edited and got the question on there, can't remove the long stupid coding stuff though, its not on edit mode.

Check the sum of r.

Reply 4

ckfeister

Original post by Pangol

It looks like you are using the wrong expression for the sum of the integers (you've used the expression for the sum of the squares of the integers again).

What one am I meant to use?

Reply 5

Pangol

Original post by ckfeister

What one am I meant to use?

Erm... the correct one...

As they are given in formula books, there's no harm in writing them out here;

sum of the first n integers = 1/2 n (n + 1)

sum of the first n squares = 1/6 n (n + 1) (2n + 1)

Reply 6

ckfeister

Original post by Pangol

I'm not doing a practise paper, I do homestudying with cloudlearn its my first time doing it.

Reply 7

Pangol

Original post by ckfeister

I'm not doing a practise paper, I do homestudying with cloudlearn its my first time doing it.

Fair enough, but you did nave the correct expression for the sum of the first six squares, so it didn't seem an outrageous assumption that you would also have seen the expression for the sum of the first six integers. In any case, they clearly cannot be the same, which is what your working would suggest.