what does i mean as if it say 9i

I assume you are dealing with square roots and radicals. You use the i when the number you are square rooting is negative.There cannot be a negative while square rooting so i is for imaginary number. Don't let that confuse you though. It's basically -1. For example; 

 √-81
-1 x 81 = -81. Take out the -1. (our i)
 √81 = 9 
We then put our i after the 9 to get 9i. 

Just one more for ya
 √-75
-1 x 75 = -75. Take out the -1 (i) again.
 √75 = 25 x 3
 √25 = 5
5i √3
The i goes on the number outside of the radical. 
Hope this helps!

i could just be a veariable like x or y or a

 

or

 

i could be an imaginary number equalling sqrt(-1)

 

so 9i = 9*sqrt(-1)