Determine if each of the following functions is $O(x^2)$.
Answer Y for yes and N for no.

 1. $f(x)= \frac{x^4}{2}$
 2. $f(x)= x \log(x)$
 3. $f(x)= \lfloor x \rfloor \cdot \lceil x \rceil$
 4. $f(x)= x^2 + 1000$
 5. $f(x)= \log(2^x)$
 6. $f(x)=17x + 11$
 7. $f(x)= 2^x$