tìm x a,5x(x-1)+x(x+17)=0 b,x(5x^2+6)-x(4x^2+6)=0 c,3x(x-3)^2-3x(x+3)^2=0

0 bình luận về “tìm x a,5x(x-1)+x(x+17)=0 b,x(5x^2+6)-x(4x^2+6)=0 c,3x(x-3)^2-3x(x+3)^2=0”

1. Đáp án:

   a, 5x(x-1)+x(x+17)=0 

   ⇔ 5x² – 5x + x² + 17x = 0

   ⇔ 6x² + 12x = 0

   ⇔ 6x(x + 2) = 0

   TH1: 6x=0

   ⇒x=0

   TH2: x + 2=0

   ⇒x=-2

   Vậy x ∈ { 0 ; – 2 }
   b, x(5x²+6)-x(4x²+6)=0
   

   ⇔ 5x³ + 6x – 4x³ – 6x = 0

   ⇔ x³ = 0

   ⇔ x = 0

   c, 3x(x-3)²-3x(x+3)²=0

   ⇔ 3x [ ( x – 3 )² – ( x + 3 )² ] = 0

   ⇔ 3x (x – 3 – x – 3 )(x – 3 + x + 3  ) = 0

   ⇔ ( – 6 ).3x.2x = 0

   ⇔ – 36x² = 0

   ⇔ x = 0

    

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2. a,5x(x-1)+x(x+17)=0 

   ⇔ 5x² – 5x + x² + 17x = 0

   ⇔ 6x² + 12x = 0

   ⇔ 6x(x + 2) = 0

   ⇔ \(\left[ \begin{array}{l}x=0\\x=-2\end{array} \right.\) 

   Vậy x ∈ { 0 ; – 2 }
   b,x(5x^2+6)-x(4x^2+6)=0
   

   ⇔ 5x³ + 6x – 4x³ – 6x = 0

   ⇔ 4x³ = 0

   ⇔ x = 0

   c,3x(x-3)²-3x(x+3)²=0

   ⇔ 3x [ ( x – 3 )² – ( x + 3 )² ] = 0

   ⇔ 3x (x – 3 + x + 3  )(x – 3 – x – 3 ) = 0

   ⇔ 3x . 2x . ( – 6 ) = 0

   ⇔ – 36x² = 0

   ⇔ x = 0

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