Tìm x 1) (x + 7)^2 – x(x – 3) = 12 2) (2x + 3)^2 – 4x^2 = 10 3) (x + 2)^2 – (x – 2) (x + 1) = 3 4) 27x^2 (x + 1) – (3x + 1)^3 = -8 5) (2x + 3)^3 –

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2. Đáp án:

    

   Giải thích các bước giải:

   $1) (x+7)^2-x(x-3)=12$

   $⇔x^2+14x+49-x^2+3x=12$

   $⇔17x=-37$

   $⇔x=-\dfrac{37}{17}$

   $2) (2x+3)^2-4x^2=10$

   $⇔4x^2+12x+9-4x^2=10$

   $⇔12x=1$

   $⇔x=\dfrac{1}{12}$

   $3) (x+2)^2-(x-2)(x+1)=3$

   $⇔x^2+4x+4-(x^2+x-2x-2)=3$

   $⇔x^2+4x-x^2+x+2=-1$

   $⇔5x=-3$

   $⇔x=-\dfrac{3}{5}$

   $4) 27x^2(x+1)-(3x+1)^3=-8$

   $⇔27x^3+27x^2-27x^3-27x^2-9x-1=-8$

   $⇔-9x=-7$

   $⇔x=\dfrac{7}{9}$

   $5) (2x+3)^2-4(x-1)^2=0$

   $⇔4x^2+12x+9-4(x^2-2x+1)=0$

   $⇔4x^2+12x-4x^2+8x-4=-9$

   $⇔20x=-5$

   $⇔x=-\dfrac{1}{4}$

   $6) (x+1)(x^2-x+1)-x(x^2-2)=4$

   $⇔x^3+1-x^3+2x=4$

   $⇔2x=3$

   $⇔x=\dfrac{3}{2}$

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