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Definition of the Average Value of a Function on an Interval: If $f$ is integrable on the closed interval [a, b], then the average value of $f$ on the interval is
$$ f(c)=\frac 1 {b-a}\int_a^bf(x)dx $$
Therefore, by using this formula, we can yield out the average value of a function or an average slope of a function. [just by derivate it) [the net accumulation]