If is zero in the interval then in this interval it is
Increasing function
Decreasing function
Only for and , is increasing function
None of the above
None of the above
Explanation for correct option:
It is given that is zero in the interval .
is a constant function.
We know that if a function is monotonic, then its value must change according to its monotonicity.
But we obtained . i.e., is a constant function.
So, the options A, B, and C are incorrect.
Hence, the correct option is D.