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# quick fp1 question Watch

1. Hi all,a quick question in the sigma and summation topic.Say if in sigma notation if r=3 bottom and r=Infinity on top.How would u solve ut?Just generally how do u solve infinuty summation?Thanks!
2. (Original post by CrazyFoxes)
Hi all,a quick question in the sigma and summation topic.Say if in sigma notation if r=3 bottom and r=Infinity on top.How would u solve ut?Just generally how do u solve infinuty summation?Thanks!
AFAIK, the only way infinity summations are going to pop in FP1 is if they are geometric sums, in which case you can just use the formula in the C1 part oft the booklet.
3. In case you are doing OCR and it comes up in method of differences.

Then you have 2 options.

Do the sum from 1 to infinity and subtract that first 2 terms (sum from 1 to 2) to leave the sum from 3 to infinity.

Or re do the method of differences starting with n = 3.

In both cases as n gets larger 1/n approaches zero, so you can ignore any terms with n at the bottom of a fraction.
4. Thanks this is really helpful.

I have 2 more topics which i still must do and i find the book and mark scheme useless.

I need help/revision on when their is a quadratic/cubic equation and they telli to substitute something and then part c to find a value ...

Also simultaneous eq. 3 unknowns and 3eq. i cant do.Examsolutions dont cover it =(

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