Hello derek445

Welcome to Math Help Forum!Question 1:

has one complete cycle every . As goes from to goes from to , and so will have complete cycles.

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Question 2:

To find the meaning of , you give the values (one at a time) in the expression after the sign, and add the results together. ( is the Greek letter corresponding to 'S', standing for the word 'sum'.)

So:

Grandad

PS In future, please post your questions one at a time - then it's easier to get them in the appropriate forum.