Toán Lớp 8: Tìm x biết
a) (x – 2)(x^2 + 2x + 4) – x( x^2 +2) = 12
b) (x – 3)^2 – (x+2)(x–2) = 16
c) x^3 – 9x = 0
d) x^3 – 6x^2 + 9x – 54 = 0
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Toán Lớp 8: Tìm x biết
a) (x – 2)(x^2 + 2x + 4) – x( x^2 +2) = 12
b) (x – 3)^2 – (x+2)(x–2) = 16
c) x^3 – 9x = 0
d) x^3 – 6x^2 + 9x – 54 = 0
Comments ( 2 )
→ x³ – 2³ – x³ – 2x = 12
→ -8 – 2x = 12
→ 2x = -20
⇒ x = -10
b) (x-3)² – (x+2)(x-2) = 16
x² – 6x + 9 – x² + 4 = 16
→ -6x + 13 = 16
→ -6x = 3
⇒ x = -0,5
c) x^3 – 9x = 0
→ x (x²-3²) = 0
→ x(x-3)(x+3) = 0
⇒ x ∈ {0; 3; -3}
d) x³ – 6x² + 9x – 54 = 0
→ x²(x+6)−9(x+6)=0
→ (x+6)(x²−9)=0
→ (x+6)(x+3)(x−3)=0
⇒ x ∈ {-6; -3; 3}
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