Đáp án:
Giải thích các bước giải:
$7.x^2-12x+11=0$
$(=)(x-1)(x-11)=0$
\(\left[ \begin{array}{l}x=1\\x=11\end{array} \right.\)
$8.x^2+8x+7=0$
$(=)(x+7)(x+1)=0$
\(\left[ \begin{array}{l}x=-7\\x=-1\end{array} \right.\)
$9.4x^2-4x-3=0$
$(=)4x^2+2x-6x-3=0$
$(=)2x(2x+1)-3(2x+1)=0$
$(=)(2x-3)(2x+1)=0$
\(\left[ \begin{array}{l}2x-3=0\\2x+1=0\end{array} \right.\)
(=)\(\left[ \begin{array}{l}x=\dfrac{3}{2}\\x=\dfrac{-1}{2}\end{array} \right.\)
$10.4x^2+12x+5=0$
$(=)(2x+5)(2x+1)=0$
\(\left[ \begin{array}{l}2x+5=0\\2x+1=0\end{array} \right.\)
(=)\(\left[ \begin{array}{l}x=-\dfrac{5}{2}\\x=-\dfrac{1}{2}\end{array} \right.\)
$11.4x^2-12x-7=0$
$(=)4x^2+2x-14x-7=0$
$(=)(2x+1)(2x-7)=0$
\(\left[ \begin{array}{l}2x+1=0\\2x-7=0\end{array} \right.\)
(=)\(\left[ \begin{array}{l}x=-\dfrac{1}{2}\\x=\dfrac{7}{2}\end{array} \right.\)
