I have the summation x(1/2)^x for (x=1,2,3,4,...)(adsbygoogle = window.adsbygoogle || []).push({});

So I set it up as s=1(1/2)+2(1/4)+3(1/8)+4(1/16)...

This is however where I'm lost, I'm not exactly sure how to sum an infinite sequence, it hasn't really been introduced in any of my math courses, it just popped up in a statistics problem though.

The book shows the next step as 1/2s=1/4+2(1/8)+3(1/16)...

then

1/2s=1/2+1/4+1/8+1/6+...=1

Thus s=2

But I'm not sure exactly what they are doing in the first & second step there. Any explanations would be helpful.

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# Homework Help: Summation x(1/2)^x

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