TuruNan
F naik
F turun

fungsi
f(x) =  - sin² x
turunan  f'(x) = 0

- 2 sin x cos x  = 0
-  sin (2x) = 0
sin(2x) = 0 = sin 0
2x= 0 + k. 2π   atau  2x = π +  k. 2π
x = 0 +  k. π    atau  x =  π/2 +  k. π
k= 0, x = 0 , x = π/2
k = 1 , x= π ,  x =  3π/2
k = 2 , x = 2π , x=  5π/2

garis bilangan f'(x) untuk  0 ≤ x  ≤  2π
[0]   - -  [ π/2]  + +  [π]   - -   [3π/2] + +  [2π]

a) interval naik f'(x) > 0  (positif)
π/2 ≤ x ≤ ≤π   dan  3π/2 ≤  x ≤ 2π

b)  interval turun  f'(x) < 0 (negatif)
0 ≤x ≤ π/2  dan  π ≤x ≤ 3π/3