$BC$ ABC $CP,$

$C({}_C).(,E,2$

$$ I $.)$

a$)E{L}^{\text{'}\text{'}}=M.$

b$)$ Castigliano $$ Castigliano $.$

${}_i=\frac{\text{d}\text{e}\text{l}\text{u}}{del{P}_i}=\frac{\text{d}\text{e}\text{l}}{del{P}_i}{\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{M^2}{2EI}dx={\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}(\frac{M}{EI})(\frac{\text{d}\text{e}\text{l}\text{M}}{del{P}_i})dx$

C$).$