the autosum feature automatically adds number in the selected cells.
its is present in standard toolbar.
why is necessary to auto-save
Alt + +
A sum just means adding things up.
An angle sum is the sum (in degrees) of the particular angles you are measuring.
Because by definition, there sum will always be zero. Because the definition of opposites are additive inverses.
By definition, they must sum to 90 degrees.
By definition, the sum must be unity.
a3 + b3
the average, the sum