Fungsi f(x) =x³-mx²-nx+2 naik pada interval x<-3 atau x>5 nilai m+n =

f(x) = x^3 -mx^2 -nx +2
f' (x) = 3x^2 -2mx -n.
untuk x = -3 => 3(-3)^2-2m(-3)-n = 0
27 +6m - n = 0...
6m - n = -27....(1)
untuk x = 5 => 3(5)^2-2m.5 - n = 0
75 -10m - n = 0
-10m - n = -75
10m + n = 75
6m - n = -27....(1)
-------------------- +
16m = 48
m = 48/16
m = 3
dari (1), 6m - n = -27
6.3 -n = 27
18 - n = 27
n = 18 -27
n = -9
maka m + n = 3 + -9 = -6