The day length, in minutes, of the $n^{\text{th}}$ day of the year in Juneau, Alaska, is given by the following function:
$D(n)=357\cos(0.02n-2.9)+740$
**What is the instantaneous rate of change of the day length on the $20^{\text{th}}$ day of the year?**
[[☃ radio 1]]
**In what units is this rate of change measured?**
[[☃ radio 2]]