Tìm x , biết : a) ( x + 7 )^2 – x ( x – 3 ) = 12 b) ( 2x + 3 )^2 – 4x^2 =10

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1. a)(x+7)²-x(x-3)=12

   x²+14x+49-x²+3x=12

   17x+49=12

   17x=12-49

   17x=-37

   x=-37:17

   x=$\frac{-37}{17}$ 

   b)( 2x + 3 )²- 4x² =10

   4x²+12x+9-4×2=10

   12x+9=10

   12x=10-9

   12x=1

   x=1:12

   x=$\frac{1}{12}$ 

    

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2. `a)(x+7)^2-x(x-3)=12.`

   `⇒x^2+2.x.7+7^2-x.x-x.(-3)=12.`

   `⇒x^2+14x+49-x^2+3x=12.`

   `⇒(x^2-x^2)+(14x+3x)+49=12.`

   `⇒17x+49=12.`

   `⇒17x=12-49.`

   `⇒17x=-37.`

   `⇒x=-37/17.`

   `b)(2x+3)^2-4x^2=10.`

   `⇒(2x)^2+2.2x.3+3^2-4x^2=10.`

   `⇒4x^2+2.2x.3+3^2-4x^2=10.`

   `⇒4x^2+12x+9-4x^2=10.`

   `⇒(4x^2-4x^2)+12x+9=10.`

   `⇒12x+9=10.`

   `⇒12x=10-9.`

   `⇒12x=1.`

   `⇒x=1/12.`

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