性质2对于任何事件A,有 P(4)=1-P(A) 证因为A∪A=9,且AA=团 所以P(4+)=P(2)=1 并且P(4+)=P()+P(A 由以上两式可得,P(4+P(4)=1 即 P(A)=1-P(4)性质2 对于任何事件A,有 P(A) = 1− P(A). 证 因为 A A AA  =  =  , . 且 所以 P(A+ A) = P() = 1 . 并且 P(A+ A) = P(A)+ P(A) 由以上两式可得, P(A) + P(A) = 1 即 P(A) = 1− P(A)