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

Find the intervals in which the function: f(x) = sin^4 x + cos^4x, 0 lex le pi/2 is strictly increasing or decreasing.

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

Find the intervals in which f(x) = sin x - cos x , 0 lt x lt 2pi , is strictly increasing or strictly decreasing.

Find the intervals in which f(x) = sin x - cos x , where 0 < x< 2pi , is strictly increasing or decreasing.

Find the intervals in which the function f given by f(x) =sin x +cos x , lt=x lt=2pi is increasing or 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 f given by f(x) =sin x +cos x , 0lt=x lt=2pi is increasing or decreasing.