The function $$f(x)=[x]$$, where $$[x]$$ denotes the greatest integer less than or equal to $$x$$, is continuous at:

If $$x=A \cos 4 t+B \sin 4 t$$, then $$\frac{d^2 x}{d t^2}$$ is equal to:

The interval in which the function $$f(x)=2 x^3+9 x^2 +12 x-1$$ is decreasing is :

$$\int \frac{\sec x}{\sec x-\tan x} d x$$ equals: