I don't understand how the integration of 4/(2x+1) is 4/2lnl(2x+1)l and not 4lnl(2x+1)l. where does the denominator 2 come from?

Answer 1

let u=2x1+1
then du = 2 dx
4/(2x+1) = 2/(2x+1) * 2dx = 2/u du