If f(c)=c^2 and c is a positive integer, which of the following CANNOT be the value of f(f(c))? Pick one.
A) 81
B) 16
C) 300
D) 256
E) 625
f(c)=c^2   f(f(c)) = (c^2)^2 = c^4   Therefore f(f(c)) will be numbers that are 4th power of other numbers.   Checking the options:   81 = 3^4   16 = 2^4   300. This cannot be written as the 4th power of any number   256 = 4^4   625 = 5^4   Answer: 300
<result>C</result>
If f(c)=c^2 and c is a positive integer, which of the following CANNOT be the value of f(f(c))?