If f(2x) = 4x² + 1, then for how many real values of x will f(2x) be the GM of f(x) and f(4x)?  

lf f(x) = [x]² - 30[x] + 221 = 0, where [x] is the greatest integer function, then what is the sum of all integer solutions? 

f f(x) = 9x - 8√x such that g(x) = f(x) - 1, then which one of the following is correct?

What is $\rm \lim\limits_{x\rightarrow \frac{\pi}{2}}(\sec \theta-\tan \theta)$ equal to?