#### decathlonist

I was studying for the test and I ran into the problem that I can't solve.

This problem involves the use of Calculus (in particular - integration). Although I do have a solution for the problem, I don't have any explanation for it. Can someone please tell me how we arrived to the final answer?

"A rod of length L and linear mass density

*l*(x)=Ax kg/m, where A is a constant and x is measured in meters from one end of the rod. Assuming the rod is in a uniform gravitational field, determine the location of the center of the rod."

( center of gravity = 2L/3 )

Thank you