Đáp án:
1) $A=-3x^2-2x-3$
2) $x=-\dfrac{1}{8}$
Giải thích các bước giải:
1)
$A=(x+1)^2-(x-1)^2-3(x+1)(x+1)$
$A=x^2+2x+1-x^2+2x-1-3(x^2+2x+1)$
$A=4x-3x^2-6x-3$
$A=-3x^2-2x-3$
2)
$\Rightarrow (x+4)^2-(x-1)(x+1)=16$
$\Rightarrow(x+4)^2-(x^2-1^2)=16$
$\Rightarrow (x+4)^2-x^2+1=16$
$\Rightarrow (x+4)^2-x^2=15$
$\Rightarrow x^2+2x.4+4^2-x^2=15$
$\Rightarrow 8x+16=15$
$\Rightarrow 8x=-1$
$\Rightarrow x=-\dfrac{1}{8}$
