# Math Help - Need help in determing gradient of this function?

1. ## Need help in determing gradient of this function?

I am trying to determine what day of the year the length of the day is increasing the most rapidly. I have collected the data, modelled a graph and acquired the function: y=155.5*cos1.1457x + 1182.8

I understand that the length of the day increasing the most will be when the gradient will be at it's highest, but I don't know what to do once I've gotten the equation.

2. Originally Posted by eriiin
I am trying to determine what day of the year the length of the day is increasing the most rapidly. I have collected the data, modelled a graph and acquired the function: y=155.5*cos1.1457x + 1182.8

I understand that the length of the day increasing the most will be when the gradient will be at it's highest, but I don't know what to do once I've gotten the equation.

First of all, what do your $x$ and $y$ represent?
So you will need to differentiate this derivative again (i.e. find the second derivative), set it equal to 0, solve for $x$.