Đáp án+giải thích các bước giải:
$1. (x+5)² -x² -8 =11$
$⇔x^2+10x+25-x^2-8=11$
$⇔10x=11+8-25$
$⇔10x=-6$
$⇔x=\dfrac{-6}{10}$
$⇔x=\dfrac{-3}{5}$
$\text{Vậy x=}$$\dfrac{-3}{5}$
$2. (x+7)² -x(x+2) =13$
$⇔x^2+14x+49-x^2-2x=13$
$⇔12x=13-49$
$⇔12x=-36$
$⇔x=\dfrac{-36}{12}$
$⇔x=-3$
$\text{Vậy x=-3}$
$3. (x+3)² -x² +4x =15$
$⇔x^2+6x+9-x^2+4x=15$
$⇔10x=15-9$
$⇔10x=6$
$⇔x=\dfrac{6}{10}$
$⇔x=\dfrac{3}{5}$
$\text{Vậy x=}$$\dfrac{3}{5}$
$4. (x+9)² -x(x-4) =21$
$⇔x^2+18x+81-x^2+4x=21$
$⇔22x=21-81$
$⇔22x=-60$
$⇔x=\dfrac{-60}{22}$
$⇔x=\dfrac{-30}{11}$
$\text{Vậy x=}$$\dfrac{-30}{11}$
$5. ( 2x + 1 )² - 4x² + 2x =-31$
$⇔4x^2+4x+1-4x^2+2x=-31$
$⇔6x=-31-1$
$⇔6x=-32$
$⇔x=\dfrac{-32}{6}$
$⇔x=\dfrac{-16}{3}$
$\text{Vậy x=}$$\dfrac{-16}{3}$
