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x² + 5x - 2 = 0
x₁ + x₂ = -b/a = -5
x₁x₂ = c/a = -2
= (x₁ + 2x₂)(x₂ + 2x₁)
= x₁x₂ + 2x₁² + 2x₂² + 4x₁x₂
= (-2) + 2{(x₁ + x₂)² - 2x₁x₂} + 4(-2)
= -2 + 2{(-5)² - 2(-2)} - 8
= -10 + 2{25 + 4}
= -10 + 2{29}
= -10 + 58
= 48
(x1 + 2x2) (x2 + 2x1) = x1.x2 + 2x²1 + 2.x²2 + 4.x1.x2
= 5.x1.x2 + 2(x²1 + x²2)
= 5.x1.x2 + 2 {(x1 + x2)² - 2.x1.x2}
= 5.x1.x2 + 2 (x1 + x2)² - 4.x1.x2
= x1.x1 + 2(x1 + x2)²
= c/a + 2 (- b/a)²
= - 2/1 + 2 (- 5/1)²
= - 2 + 2 . 25
= - 2 + 50
= 48
3) 3x² + 5x - 6 = 0 ⇒ a = 3 ; b = 5 ; c = - 6
α + β = (3x1 - 2) + (3x2 - 2)
= 3x1 + 3x2 - 4
= 3 (x1 + x2) - 4
= 3 (- b/a) - 4
= 3 (- 5/3) - 4
= - 5 - 4
= - 9
α.β = (3.x1 - 2) (3.x2 - 2)
= 9.x1 .x2 - 6.(x1 + x2) + 4
= 9 .(c/a) - 6 (- b/a) + 4
= 9 .( - 6/3) - 6 ( - 5/3) + 4
= - 18 + 10 + 4
= - 4
bentuk umum persamaan baru :
x² - (α + β) x + α .β = 0
x² - (-9)x + (- 4) = 0
x² + 9x - 4 = 0