1 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)}

The perimeter of △cde is 55 cm. a rhombus dmfn is inscribed in this triangle so that vertices m, f, and n lie on the sides cd , ce , and de respectively. find cd and de if cf=8 cm and ef=12 cm. the answer is not cd=20 and de=15. i have tried that one, it does not work.