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x^2 + x + 6 = 0
(x + 3) (x - 2) = 0
x = -3
x = 2
f(x) = x^3 - 3x^2 + ax + b
Cari persamaan dengan cara mensubtitusikan x
a. Cara persamaan pertama
f(-3) = (-3)^3 - 3(-3)^2 + a(-3) + b
15x - 9 = -27 - 3(9) - 3a + b
15(-3) - 9 = -27 - 27 - 3a + b
-45 - 9 = -54 - 3a + b
-54 = -54 - 3a + b
-54 + 54 = -3a + b
0 = -3a + b
0 = 3a - b
3a - b = 0 (Persamaan 1)
b. Cari Persamaan yang kedua
f(2) = (2)^3 - 3(2)^2 + a(2) + b
15x - 9 = 8 - 3(4) + 2a + b
15(2) - 9 = 8 - 12 + 2a + b
30 - 9 = -4 + 2a + b
21 = -4 + 2a + b
21 + 4 = 2a + b
25 = 2a + b
2a + b = 25 (Persamaan 2)
Gunakan Eliminasi
3a - b = 0
2a + b = 25 + (Ditambah)
5a = 25
a = 25 / 5
a = 5
Subtitusikan a ke salah satu persamaan
3a - b = 0
3(5) = b
15 = b
b = 15
a + b = 5 + 15
a + b = 20
Selesai. Semoga bermanfaat