Finding the Average Rate of Change for a Trig Function on a Given Interval

[DespicableMe]

Homework Statement

Determine the average rate of change of the function y = 2cos (x - pi/3) + 1 for the following internal:
pi/2 < x < 5pi/4

Homework Equations

AROC = [ f(x₂) - f(x₁) ] / x₂) - x₁

The Attempt at a Solution

For an approx. value, I would set the calculator in radian mode and just plug everything into the equation, right?
Where I'm stuck is how to get an EXACT answer.

 

[armolinasf]

If you're trying to find the average rate of change, I'm assuming that the interval would be pi/2 and 5pi/4 and those would be your x1 and x2 values.

To get an exact answer have to evaluate y at both your x1 and x2 values then fill out the slope equation:

{[2cos (5pi/4 - pi/3) + 1]*[2cos (pi/2 - pi/3) + 1]}/(5pi/4-pi/2)

Hope this helps