1. *
2 points
Which relation is not a function?
1) {(1,5),(2,6),(3,6),(4,7)}
2) {(4,7),(2,1),(-3,6),(3,4)}
3) {(-1,6),(1,3), (2,5),(1,7)}
4) {(-1,2),(0,5),(5,0),(2,-1)}