Đáp án:
$\begin{array}{l}
c)3{x^2} + 7x + 2 = 0\\
\Leftrightarrow 3{x^2} + x + 6x + 2 = 0\\
\Leftrightarrow \left( {3x + 1} \right)\left( {x + 2} \right) = 0\\
\Leftrightarrow x = - \dfrac{1}{3};x = - 2\\
Vậy\,x = \dfrac{{ - 1}}{3};x = - 2\\
d){x^2} - 2x + 2 = 0\\
\Leftrightarrow {x^2} - 2x + 1 + 1 = 0\\
\Leftrightarrow {\left( {x - 1} \right)^2} + 1 = 0\left( {vn} \right)
\end{array}$
Vậy pt vô nghiệm.
$\begin{array}{l}
B3)\\
a)m = 5\\
\Leftrightarrow {x^2} - 16x + 28 = 0\\
\Leftrightarrow {x^2} - 14x - 2x + 28 = 0\\
\Leftrightarrow \left( {x - 14} \right)\left( {x - 2} \right) = 0\\
\Leftrightarrow x = 14;x = 2\\
Vậy\,x = 14;x = 2\\
b)\Delta ' = 0\\
\Leftrightarrow {\left( {m + 3} \right)^2} - {m^2} - 3 = 0\\
\Leftrightarrow {m^2} + 6m + 9 - {m^2} - 3 = 0\\
\Leftrightarrow 6m = - 6\\
\Leftrightarrow m = - 1\\
Khi:m = - 1\\
\Leftrightarrow {x^2} - 4x + 4 = 0\\
\Leftrightarrow {\left( {x - 2} \right)^2} = 0\\
\Leftrightarrow x = 2\\
Vậy\,x = 2\\
B4)\\
a)m = 11\\
\Leftrightarrow 9{x^2} + 22x + 8 = 0\\
\Leftrightarrow 9{x^2} + 18x + 4x + 8 = 0\\
\Leftrightarrow \left( {x + 2} \right)\left( {9x + 4} \right) = 0\\
\Leftrightarrow x = - 2;x = - \dfrac{4}{9}\\
Vậy\,x = - 2;x = \dfrac{{ - 4}}{9}\\
b)\left\{ \begin{array}{l}
m - 2\# 0\\
\Delta ' > 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
m\# 2\\
{m^2} - \left( {m - 2} \right)\left( {m - 3} \right) > 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
m\# 2\\
{m^2} - {m^2} + 5m - 6 > 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
m\# 2\\
m > \dfrac{6}{5}
\end{array} \right.\\
Vậy\,m > \dfrac{6}{5};m\# 2
\end{array}$
