Which relation is a function?

If there is no real number solution to the quadratic equation x^2+2x+c=0 what is a possible value of c? 1 -2 0 3

The ratios 3: 9, 4: 12, 5: 15, and 6: 18 are a pattern of equivalent ratios in the ratio table. which is another ratio in this pattern?

For the sequence [tex]a_{n} = 2n/(n+1)[/tex], what is the value of [tex]a_{10}[/tex]