Let F(a) be the area between the x-axis and the graph of y=x^2cos(x/4) between x=0 and x=a, for a0 (consider the area to be negative if the graph lies below the axis).

Question

Let F(a) be the area between the x-axis and the graph of y=x^2cos(x/4) between x=0 and x=a, for a>0 (consider the area to be negative if the graph lies below the axis). 
Find a formula for F(a).