jika (m, 3n) adalah penyelesaian sistem persamaan kuadrat y = 2x² + 5x + 8 y = x² - 5x - 17 nilai 2m - n adalah = .... a. -43 b. -23 c. -21 d. -11 e. -8 Diketah

pakai substitusi
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2x² + 5x + 8 = x² - 5x - 17
2x² - x² + 5x + 5x + 8 + 17 = 0
x² + 10x + 25 = 0
(x + 5)(x + 5) = 0
x = -5
y = -5² - 5(-5) - 17
y = 25 + 25 - 17
y = 33
(m , 3n) = (-5 , 33)
m = -5
3n = 33
n = 11
2m - n = 2(-5) - 11 = -10 - 11 = -21

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2x² - 3x + 6 = x² + 5x - 6
2x² - x² - 3x - 5x + 6 + 6 = 0
x² - 8x + 12 = 0
(x - 6)(x - 2) = 0
x = 6 dan x = 2
x = 6 --> y = 6² + 5(6) - 6 = 36+30-6 = 60
x = 2 --> y = 2² + 5(2) - 6 = 4+10-6 = 8
(a,b) = (6,60)
(c,d) = (2,8)
b + d = 60 + 8 = 68