Harap bantuannya tentang keuntungan maksimum soal tertera digambar

Biaya per unit = (5x^2 - 21/2 x + 32) ribu
Biaya x unit = x(5x^2 - 21/2 x + 32) ribu
= (5x^3 - 21/2 x^2 + 32x) ribu

Harga jual tiap unit = 50.000 = (50)ribu
Harga jual x unit = x(50) ribu = (50x) ribu

Keuntungan = harga jual - biaya
U = 50x - (5x^3 - 21/2 x^2 + 32x)
U = -5x^3 + 21/2 x^2 + 18x
U' = -15x^2 + 21x + 18 = 0
=> -3(5x^2 - 7x - 6) = 0
=> -3(5x + 3)(x - 2) = 0
x = -3/5 atau x = 2
Garis bilangan
--- (-3/5) +++ (2) ---
Karena maksimum maka x = 2
U = -5x^3 + 21/2 x^2 + 18x
= -5(2)^3 + 21/2 . 2^2 + 18(2)
= -40 + 42 + 36
= 38 ribu rupiah
= Rp38.000,00