SOLUTION: Is there an easy way to memorize the formulas for geometric and arithmetic series & sequences and to figure out a specific term?

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Question 874159: Is there an easy way to memorize the formulas for geometric and arithmetic series & sequences and to figure out a specific term?
Answer by richwmiller(17219)   (Show Source): You can put this solution on YOUR website!
It helps if you understand what they mean and have used them a few times.
Arithmetic
if you know the last term use S = ½(a + an)n
S = ½(2a + (n-1)d)n
an = a + (n - 1)d

Geometric
Tn = t * r^(n - 1)
S=t*(1 - r^n)/(1 - r)

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