Question 266763
I hope I can help you here.
The first term, a1 = 1/5
the common ratio = -1.
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From here not sure what you want:
91st term =1/5
formula is
Tn = (1/5)*(-1)^(n-1)
The infinite sum is a/(1-r) = (1/5) / (1-1/5) = 1/4
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hopefully one of these is what you wanted