819200sec^4(8x)(sec(8x)tan(8x))=819200sec^5(8x)tan(8x).
Let y=sec(8x), dy/dx=8sec(8x)tan(8x);
let z=y^5, dz/dx=dz/dy*dy/dx=5y^4dy/dx=(5sec^4(8x))(8sec(8x)tan(8x))=40sec^5(8x)tan(8x);
let w=20480z;
dw/dx=dw/dz*dz/dy*dy/dx=20480*40sec^5(8x)tan(8x)=819200sec^5(8x)tan(8x).