Jawab:
y = (x + 2)(x - 1)(x - 4)
0 = (x + 2)(x - 1)(x - 4)
maka titik potong sumbu x
A(-2, 0)   B(1, 0)   C(4, 0)
Lalu cari turunan (y')
y' = (x+2)'(x-1)(x-4) + ((x-1)(x-4))'(x+2)
y' = 1(x-1)(x-4) + (x²-5x+4)'(x+2)
y' = (x²-5x+4) + (2x-5)(x+2)
y' = (x²-5x+4) + (2x²-x-10)
y' = 3x²-6x-6
Lalu cari pembuat 0 dari y'
3x²-6x-6 = 0
x²-2x-2 = 0
x²-2x = 2
x²-2x+(2/2)² = 2+(2/2)²
x²-2x+1 = 2+1
x²-2x+1 = 3
(x-1)² = 3
x-1 = ±√3
x = 1+√3  dan  1-√3
Masukkan x
y = (1+√3 + 2)(1+√3 - 1)(1+√3 - 4)
y = (3+√3)(√3)(-3+√3)
y = (3√3+3)(-3+√3)
y = -9√3+9-9+3√3
y = -6√3
D (1+√3, -6√3)
atau
y = (1-√3 + 2)(1-√3 - 1)(1-√3 - 4)
y = (3-√3)(-√3)(-3-√3)
y = (-3√3+3)(-3-√3)
y = 9√3+9-9-3√3
y = 6√3
E (1-√3, 6√3)
y' = 3x²-6x-6 < 0
maka fungsi turun antara
titik E dan D

Cari titik potong dgn sumbu y
x = 0, maka
y = (0 + 2)(0 - 1)(0 - 4)
y = 2(-1)(-4)
y = 8
F (0, 8)

<(7o7)>