card A= card A\B + card (A∩B)
deci
cardA≥card A\B
cardA*card A\B=14 =14*1=7*2
14= 14*1
caz I
card A=14, card A\B=1
card A= card A\B + card (A∩B)
14=1+card (A∩B)
card A∩B=13
caz II
card A=7 , card (A\B)=2
cardA= card (A\B) +card (A∩B)
7=2+card (A∩B)
card (A∩B)=5