(1)任取y∈f(A∪B),设x->y,则x∈A∪B,x∈A或x∈B,y∈f(A)或y∈f(B),y∈f(A)∪f(B):
任取y∈f(A)∪f(B),设x->y,y∈f(A)或y∈f(B),x∈A或x∈B,x∈A∪B,y∈f(A∪B):
(2任取y∈f(A∩B),设x->y,x∈A∩B,x∈A且x∈B,
(1)任取y∈f(A∪B),设x->y,则x∈A∪B,x∈A或x∈B,y∈f(A)或y∈f(B),y∈f(A)∪f(B):
任取y∈f(A)∪f(B),设x->y,y∈f(A)或y∈f(B),x∈A或x∈B,x∈A∪B,y∈f(A∪B):
(2任取y∈f(A∩B),设x->y,x∈A∩B,x∈A且x∈B,