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Summation Formulas

The symbol Σ (sigma) is generally used to denote a sum of multiple terms. 

This symbol is generally accompanied by an index that varies to encompass all terms that must be considered in the sum.

This expression means sum the values of x, starting at x1 and ending with xn.
This expression means sum the square values of x, starting at x1 and ending with xn.

Few summation formulas are given below
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