Average Rate of Change

What is the average rate of change over the interval [5pi/4, 7pi/4] with the function f(x) = cot x?

 

7pi/4 - 5pi/4 = 2pi/4 = pi/2

 

f(7pi/4)=cot(7pi/4) = -cot(pi/4) = -1

f(5pi/4)=cot(5pi/4) = +cot(pi/4) = +1

 

f(7pi/4) - f(5pi/4) = -1-1 = -2

 

Average rate of change = -2 divided by pi/2  = -4/pi