Đáp án:
Giải thích các bước giải:
$a)(x+4)^2-(x-2)(x+2)=15$
$⇔x^2+8x+16-x^2+4=15$
$⇔8x=-5$
$⇔x=-\dfrac{5}{8}$
$b)2(x-2)^2-(x+1)^2=x(x+1)$
$⇔2(x^2-4x+4)-(x^2+2x+1)-x^2-x=0$
$⇔2x^2-8x+8-x^2-2x-1-x^2-x=0$
$⇔-11x=-7$
$⇔x=\dfrac{7}{11}$
$c)(x+7)(x-7)-(x+3)^2=x-4$
$⇔x^2-4x-x^2-6x-9-x=-4$
$⇔-11x=5$
$⇔x=-\dfrac{5}{11}$
$d)(7x+1)^2-(7x+2)(7x-2)=-25$
$⇔49x^2+14x+1-49x^2+4=-25$
$⇔14x=-30$
$⇔x=-\dfrac{15}{7}$