There is a certain relation between two given number on one side of : : and one number is given on another side of

There is a certain relation between two given number on one side of : : and one number is given on another side of : : while another number is to be found from the given alternatives, having the same relation with this number as the numbers of the given pair bear. Choose the best alternative.

9 : 79 : : 100 : ?

1. 901
2. 1009
3. 9889
4. 9998

Sol:

79=9²−2,so 100²−2=9998