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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: k. 4x^2 – 25 –( 2x -5)(2x +7)=0

Toán Lớp 8: k. 4x^2 – 25 –( 2x -5)(2x +7)=0

Comments ( 2 )

  1. $4x^2-25-(2x-5)(2x+7)=0$
    $⇔ (2x-5)(2x+5)-(2x-5)(2x+7)=0$
    $⇔ (2x-5)(2x+5-2x-7)=0$
    $⇔ (2x-5).(-2)=0$
    $⇔ x=\dfrac52$

  2. k. 4x^2 – 25 – ( 2x – 5)(2x +7) = 0
    <=>( 2x – 5)(2x + 5) – ( 2x – 5 )(2x +7) = 0
    <=>(2x – 5)(2x + 5 – 2x – 7) = 0
    <=>( -2 )( 2x  -5 ) = 0
    <=> 2x – 5 = 0
    <=> 2x = 5
    <=> x = 2/5
     

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222-9+11+12:2*14+14 = ? ( )