设0
AP(A+B|<)=P(A|
)+P(B|
)
BP(AC+BC)=P(AC)+P(BC)
CP(A+B)=P(A|C)+P(B|C)
DP(C)=P(A)P(C|A)+P(B)P(C|A)
由P(A+B|C)=P(A|C)+P(B|C),因为P(A+B|C)=P(A|C)+P(B|C)-P(AB|C),所以P(AB|C)=0,从而P(ABC)=0,故P(AC+BC)=P(AC)+P(BC)-P(ABC)=P(AC)+P(BC),选(B).
图示结构,各杆EI=常数,不计轴向变形,MBA及MCD的状况为: