§32容斥原理 A1∪A∪…An=A1∩A2…A,正确 A1UA2∪. UAUA=(AU…JA1)UA21 =(A4UA2U…UA1∩A1 =A1∩A21.An∩A1 即定理对n+1也是正确的2 1 2 ... ... A1 A A A A A n n = 正确 2 1 1 2 1 2 1 1 1 1 ... ( ... ) ( ... ... n n n n n n n n A A A A A A A A A A A A A A + + + + = = = 1 则 A 即定理对n+1也是正确的。 §3.2 容斥原理