Q: How would you derive this flexibility influence coefficent equation? ${}_{ij}=\{\begin{array}{cc}\frac{b_j{x}_i}{6\text{E}\text{I}\text{l}}(l^2-b_j^2-x_i^2),& x_i{a}_i\\ \frac{a_j(l-x_i)}{6\text{E}\text{I}\text{l}}(2l{x}_i-a_j^2-x_i^2),& x_i>a_i\end{array}$