tolong di jawab makasih

x³ - 7x - 6 = (x + 1)(x + 2)(x - 3)

... = a/(x + 1) - b/(x + 2) + c/(x - 3)

3x² - 16x + 5 = a(x + 2)(x - 3) - b(x + 1)(x - 3) + c(x + 1)(x + 2)

(a - b + c) x² = 3x²
a - b + c = 3 ... (1)

(-a + 2b + 3c) x = -16x
-a + 2b + 3c = -16 ... (2)

-6a + 3b + 2c = 5 ... (3)

Pk eliminasi substitusi atau matriks, didpt :
a = Da/D = -120/20 = -6
b = Db/D = -196/20 = -49/20
c = Dc/D = -16/20 = -4/5

Maka
a + 2b - 3c
= -6 - 49/10 + 24/10
= -6 - 5/2
= -8,5