Summation (Σ) Notation

This appears as the symbol, Σ, which is the Greek upper case letter, S. The summation sign, Σ, instructs us to sum the elements of a sequence. A typical element of the sequence which is being summed appears to the right of the summation sign.

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

This expression  means sum the values of x, starting at x1 and ending with x10.

This expression  means sum the values of x, starting at x3 and ending with x10.

This expression means sum the squared values of x, starting at x1 and ending with x