Create a MATLAB function called firstDeriv which takes the first derivative using the two-point formula. The input arguments are: step width h for the two-point formula, lower bound, and upper bound, in that order.

**The output of the function is an array of samples of the calculated derivative of the input function. The array has (upper bound - lower bound)/0.1 +1 points (given 0.1 spacing between points)**

Use it to caculate the derivative of the funciton f(x) = cos(x)