C. Determine whether each rule below represents a function or not.
1. y = 3x + 9
6. x + y2 = 10
2. y = -2x - 7
7.x = y
3. x + y = 10
8. y = x?
4. x2 + y2 = 2
9. y = 4+1
5. 2x2 + y2 = 8
10.x2 - y2 = 16​