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 –

Đáp án:

Giải thích các bước giải:

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

$⇔x^2+14x+49-x^2+3x=12$

$⇔17x=-37$

$⇔x=-\dfrac{37}{17}$

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

$⇔4x^2+12x+9-4x^2=10$

$⇔12x=1$

$⇔x=\dfrac{1}{12}$

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

$⇔x^2+4x+4-(x^2+x-2x-2)=3$

$⇔x^2+4x-x^2+x+2=-1$

$⇔5x=-3$

$⇔x=-\dfrac{3}{5}$

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

$⇔27x^3+27x^2-27x^3-27x^2-9x-1=-8$

$⇔-9x=-7$

$⇔x=\dfrac{7}{9}$

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

$⇔4x^2+12x+9-4(x^2-2x+1)=0$

$⇔4x^2+12x-4x^2+8x-4=-9$

$⇔20x=-5$

$⇔x=-\dfrac{1}{4}$

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

$⇔x^3+1-x^3+2x=4$

$⇔2x=3$

$⇔x=\dfrac{3}{2}$