Hi I am trying to derive an expression for the deflection in a cantilever beam using castigliano's theorem.
I have found and attached an example of the solution. I understand the most of what is going on in the attached solution but I don't know where the b^3 came from in the line (b)
The Attempt at a Solution
When I perform the integration from line (a) i get
L^2/6(2L-3b). Can anybody explain where the b^3 in line (b) comes from[/B]