If f(y)=y^2 and y is a positive integer, which of the following CANNOT be the value of f(f(y))?
Choices
A) 625
B) 1296
C) 256
D) 350
E) 16
f(y)=y^2   f(f(y)) = (y^2)^2 = y^4   Therefore f(f(y)) will be numbers that are 4th power of other numbers.   Checking the options:   625 = 6^4   1296 = 6^4   256 = 4^4   350. This cannot be written as the 4th power of any number   16 = 2^4   Answer: 350
<result>D</result>
If f(y)=y^2 and y is a positive integer, which of the following CANNOT be the value of f(f(y))?