What value of c would make this polynomial a perfect square? x^2 - 12x + ci really need this ! 

c = 36

Explanation:
The perfect square in case of negative middle term has a general form of:
(x-a)^2 
and is expanded as:
x^2 - 2ax + a^2
The given expression is:
x^2 - 12x + c

Comparing the given expression to the general one, we will find that:
2ax = 12x
2a = 12
a = 6

Now, comparing the two expressions again, we will find that:
c = a^2
c = (6)^2
c = 36

Therefore, when c=36, the given expression would be a perfect square factorized as (x-6)^2

Hope this helps :)