Question

determinati numarul submultimilor cu 2 elemente ale multimii {1, 2,3,4,5,6,7}

Answer 1

faci combinari de 7 luate de cate 2, trebuie sa-ti dea 21 de submultimi.

Answer 2

[1,2],[1,3],[1,4],[1,5],[1,6],[1,7],[2,3],[2,4],[2,5],[2,6],[2,7],[3,4],[3,5],[3,6],[3,7],[4,5],[4,6],[4,7],[5,6],[5,6],[6,7]⇒6+5+4+3+2+1=6·7/2=3·7=21[numarul de submultimi cu 2 elemente];