6.Tìm x,biết:a)5x(x+2)-7(x-2)=0;b)(x-5)(2x+1)-(2x-1)(x+2)=8

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1. a)5x (x+2)-7(x-2)=0

   <=> 5x (x + 2) + 7 (x + 2) = 0

   <=> (x + 2)(5x + 7) =0

   <=> \(\left[ \begin{array}{l}x=x+2=0\\x=5x+7=0\end{array} \right.\) <=>\(\left[ \begin{array}{l}x=-2\\x=-7/5\end{array} \right.\) 

   b)(x-5)(2x+1)-(2x-1)(x+2)=8

   <=> 2x^2 + x − 10x − 5 − ( 2x^2 + 4x − x − 2 ) = 8

   <=> 2x^2 + x − 10x − 5 − 2x^2 − 4x + x + 2 = 8

   <=> − 12x − 3 = 8

   <=> x = − 11/12

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