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Trying to read Simple Wikipedia's Mathematical Induction article:

https://simple.wikipedia.org/wiki/Mathematical_induction

In many of the images, like this one:
https://wikimedia.org/api/rest_v1/media/math/render/svg/8aca5140d2bef31cc6ec27c34ace175533d0685d

There is a 2 to the right sorry, left of the summation symbol. What does it mean?

G. Chiusole
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user156964
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  • It's just a multiplicative factor. You should read it as "2 times the sum of...". – Hubble Oct 03 '16 at 19:00
  • 2 * the sum of all of those numbers leading up to n (aka, 2 * n)? It's not really clicking with me... – user156964 Oct 03 '16 at 19:07
  • $2 \times \left(\sum_{k=1}^n k\right) = n(n+1)$. – Hubble Oct 03 '16 at 19:11
  • Ok, so the idea is that you keep adding up until what you're adding is the number n. And that first image I linked is rewritten from https://wikimedia.org/api/rest_v1/media/math/render/svg/0197730674f8dd57d86dbd401f9eb19fb5397e07 with the 1/2 taken from the left and added as a times 2 on the right. Thanks. – user156964 Oct 03 '16 at 19:18

1 Answers1

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If you have $a\sum_{b=1}^{c}d$, that means you multiply $a$ by $\sum_{b=1}^{c}d$. Thus, you take $2$ and multiply it by $\sum_{k=1}^{n}k$.

4yl1n
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