Thinking@TheCulture is a series of questions that we, as tutors feel that are useful in helping students think and improve their understanding.
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This is a standard summation question. I’m interested in the last part only.
Summation Question
The answer to (ii) is written there by the student. I’ll only do the solution to (iv).
with 
. This is to make the term in the summation similar, disregarding the lower and upper limit.
while upper limit is 
.
appear.
by 
directly. It will affect our RHS.
