Question

Fie D si E multimi. Daca card D x card (D\E)= 21, aflati card (D intersectat cu E)

Answer 1

card D x card (D\E)= 21,

card D * (card D-card (D∩E)=21
21=card D * (card D-card (D∩E)=21=21*1=7*3=3*7=1*21
cum card D≥card (D∩E) avem doar situatiile/solutiile

a)card D=21 card (D∩E)=20 ptca 21* (21-20)=21 cu card E min=20
si
b)card D=7  card (D∩E)=4 pt ca 7*(7-4)=7*3=21 cu card E min=4

deci solutii a)card (D∩E)=20
b)card (D∩E)=4