Question -
Answer -
Let f(x) = sin x +cos x.
Now, 
will be negative when(sin x + cos x) is positive i.e., when sin x andcos x are both positive. Also, we know that sin x andcos x both are positive in the first quadrant. Then, will be negative when
.
Thus, we consider
.
∴By second derivative test, f will bethe maximum atand the maximum valueof f is
.