Problem FEX$-02[$Points: $1/3].$ For the $2$D truss shown:

$($a$)[$Points $0\mathrm{.}5/3]$ Calculate the internal forces $F_{AD},$ and $F_{CD}$ using the method of joints.

$($b$)[$Points $0\mathrm{.}5/3]$ Calculate the internal forces $F_{AD},F_{BD},$ and $F_{BC}$ using the method of sections.