## Mathematics - useful results

##### Created by:

philippgrinev  on June 25, 2012

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# Mathematics - useful results

 Finding nth term of sequence with alternating signsPositive term first: The answer will have a multiplication by (-1)^(n+1). Negative first: The answer will have a multiplication by (-1)^n.
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#### Definitions

Finding nth term of sequence with alternating signs Positive term first: The answer will have a multiplication by (-1)^(n+1).
Negative first: The answer will have a multiplication by
(-1)^n.
Sum of an arithmetic progression The sum of n terms of an arithmetic progression with first term being a, the last l, and d the common difference is equal to (1/2)n(a+l) or (1/2)(2a+(n-1)d).
Last term of an arithmetic progression = a+(n-1)d, where a is the first term and d is the common difference of the progression.
Permutation formula nPr = (n!)/((n-r)!)
Combination formula nCr = (n!)/(r!(n-r)!)
Sum of geometric progression The sum of n terms is: S = [a(1-r^n)]/[1-r], where r is what we multiply each term by to get the next one, a is the first term of the progression.

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