sigma notation [series & sequences]
 

Hi,

I want to double check this math problem for the spring break take-home test:

q: use sigma notation to express the series: 0.2 - .8 + 3.2 - 12.8 + 51.2 - ..........

A: I realized that the powers of 2 are at odd integers, then divided by 10.

[i.e. 2^1=2
2^3=8
etc.....]

but I'm trying to figure out how to express this [the fact only odd integers are used as the powers] in notation....

so far i have:


thanks for the help,
will.

Well my first suggestion would be to put the series {1,3,5,7,9...} in sigma notation. These are the exponents you're raising two to. This is what you're hung up on, and hopefully by breaking it down this way you can do it.

Almost there, but like you say the formula you have now will give you .2-.4+.8 ...

Try this:

I'm a bit rusty and working quickly but that should work.

Actually I believe it should be:

aha - that's it !

thanks for your help ickky and elsesomebody ! :thumbsup:


catcha back on the flipside,
keyshawn

Well first of this cant be an infinite series since the sum is divergent. And also the equations presented before are somewhat difficult to work with when dealing with a sum.
Then the sum just becomes

No problem

I always wanted to answer a math problem in tilted knowledge but all these smart TFPers always beat me to it.