" The interval in which the function "f(x)=sin3x,x in[0,(pi)/(2)]" is strictly increasing "

Find the interval in which the function f(x)=sinx+cosx, 0lexle2pi is strictly increasing or strictly decreasing.

Find the intervals in which the function f(x) = sin x +cos x,x in [0, 2pi] is (i) strictly increasing, (ii) strictly decreasing.

Find the intervals in which the function given by f(x)=sin3x, x in [0, (pi)/(2)] is : (a) increasing (b) decreasing.

Find the intervals in which the function given by f(x) = sin 3x , x in [ 0, pi/2 ] is increasing.