Answer:
1. 9
2. -3
Step-by-step explanation:

Common difference of an Arithmetic progression can be found out by subtracting the preceding term from that given term.
i.e
therefore, the common difference of the above Arithmetic progression is -4 .
No you can't because there wasn't any zeros in this function.
Yup your right ( i’m just writing here so it lets me send it)