Tìm x, biết : a.) 5. ( x- 3 ) = x. ( x – 3 ) b.) x^2 – ( x – 3 ). ( x +2 ) = 1

2 bình luận về “Tìm x, biết : a.) 5. ( x- 3 ) = x. ( x – 3 ) b.) x^2 – ( x – 3 ). ( x +2 ) = 1”

1. a, 5(x – 3) = x(x – 3)

   => 5(x – 3) – x(x – 3) = 0

   => (x – 3)(5 – x) = 0

   => x – 3 = 0 hoặc 5 – x=  0

   => x = 3 hoặc x = 5

   Vậy x \in {3,5}

   b, x^2 – (x – 3)(x + 2) = 1

   => x^2 – x.x – x.2 + 3.x + 3.2 = 1

   => x^2 – x^2 – 2x + 3x + 6 = 1

   => x = 1 – 6

   => x = -5

   Vậy x = -5

   $#duong612009$

   Trả lời
2. a, 5 ( x – 3 ) = x ( x – 3 )

   <=> 5 ( x – 3 ) – x ( x – 3 ) = 0

   <=> ( x – 5 ) ( x – 3 ) = 0

   <=> $\left[\begin{matrix} x – 5 = 0\\ x – 3 = 0\end{matrix}\right.$

   <=> $\left[\begin{matrix} x = 5\\ x = 3\end{matrix}\right.$

   Vậy x in { 5 ; 3 }

   b, x^2 – ( x – 3 ) ( x + 2 ) = 1

   <=> x^2 – x^2 – 2x + 3x + 3.2 = 1

   <=> x + 6 = 1

   <=> x = -5

   Vậy x = -5

    

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