I was trying to prove lg n! = theta(n lg n)

I used the below expression to prove it

**0 <= c1(n lg n) <= lg n! <= c2(n lg n)** - equation 1

By using **lg n! <= c2(n lg n)** from the above equation, I could prove that lg n! = big O(n lg n)

however to prove lg n! = big omega(n lg n), I need to use the other part of equation 1 which is

**c1(n lg n) <= lg n!** - equation 2

can anyone help me as to how to solve equation 2 to prove big omega. The hint which I got to know is to do perform integration. But I'm not able to do it. Kindly help me out here

Thank you very much.