Consider the function f(x)=1x\displaystyle {f{{\left({x}\right)}}}={\frac{{{1}}}{{{x}}}} on the interval [2,10]\displaystyle {\left[{2},{10}\right]}. Find the average or mean slope of the function on this interval.
 

By the Mean Value Theorem, we know there exists a c\displaystyle {c} in the open interval (2,10)\displaystyle {\left({2},{10}\right)} such that f(c)\displaystyle {f}'{\left({c}\right)} is equal to this mean slope. For this problem, there is only one c\displaystyle {c} that works. Find it, and enter the exact value.