What does the sigma refer to? Is it a summation and if so, what are the limits and dummy indices?
With that "du" I'm inclined to believe you mean an integration with respect to u But then what about the "5x" and "cos(x)"? Do you mean, the simplest way I can interpret this,
? To integrate that you could use , twice. But I cannot imagine where you could have got that "20" inside the cosine, much less the cube! So perhaps I am misunderstanding completely.