Class: Fluid mechanics $////$ I need help. This definition makes absolutely zero sense in the way the solution is set up$.$ Skin friction coeff and von karman are not related, at all, in any definitions I have. The only way to relate them is to rearrange the skin friction coefficient to be in terms of shear stress so you could plug it into the von kerman equation on the left side. Look, I get the math for step $1,$ but when they introduce the von karman equation it stop making sense, because I don't understand where or how we get the relationship C$\_$f $=2*($d$($theta$)/$dx$)$

I've been studying all day, pls dont lead me in circles with this.