C$$u $2(4)$: Cho khung nhu h$$nh v$$

a$-$ T$$m c$$c g$$c xoay t$$i c$$c li$$n k$$t b$$ng pp chuy$$n v$$ thu g$$n

b$-$ T$$m c$$c ph$$n l$$c li$$n k$$t b$$ng pp ph$$n ph$$i moment

c$-$ V$$ bi$$u $$ l$$c d$$c$,$ bi$$u $$ l$$c c$$t v$$ bi$$u $$ moment cho khung