Find the least integer n such that f (x) is O(x^n) for each of these functions.

a) f (x) = 2x^2 + x^3logx

b) f (x) = 3x^5 + (logx)^4

c) f (x) = (x^4 + x^2 + 1)/(x^4 + 1)

d) f (x) = (x^3 + 5logx)/(x^4 + 1)