# Further Maths Edexcel Question (Series)Watch

#1

These types of questions I really cannot understand. I've tried multiplying out the brackets and then putting each term into n, then plugging in 20 and all dividing by 1.

This does not give me the right answer.

I've also tried splitting the fraction and using the method of differences, to no avail.

I'm probably missing something really obvious but its annoying me as its with every question in a fraction.

Help would be much appreciated =]
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9 years ago
#2
If you split it, as per partial fractions, you can write it as the difference of two sums, most of whose terms will cancel out.
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9 years ago
#3
then use the differences method. You might need to write down a few initial results like r = 1, r =2 etc before you spot what's cancelling.
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9 years ago
#4
The method of differences should work (having split it into partial fractions).
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#5
yeah i've tried that already, just made sure again now. nothing actually cancel's out i'm pretty sure. tried up to 5, and only 1 term could be cancelled out. At a loose end here...
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9 years ago
#6
Stuff does cancel, after 3 of them...
1/3 - 1/6
+
1/4 - 1/7
+
1/5 - 1/8
+
1/6 - 1/9
+
1/7 - 1/10
...
...
1/23 - 1/26
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#7
ha okay sorry, my stubborness to give up easily messed me up on this question. Thanks for your patience guys, got there in the end =]
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