a.
Em tự giải
b.
\(\Delta'=\left(m+3\right)^2-\left(m^2+3\right)=6m+6>0\Rightarrow m>-1\)
Theo hệ thức Viet: \(\left\{{}\begin{matrix}x_1+x_2=2\left(m+3\right)\\x_1x_2=m^2+3\end{matrix}\right.\)
\(\left(2x_1-1\right)\left(2x_2-1\right)=9\)
\(\Leftrightarrow4x_1x_2-2\left(x_1+x_2\right)+1=9\)
\(\Leftrightarrow8\left(m+3\right)-2\left(m^2+3\right)-8=0\)
\(\Leftrightarrow-2m^2+8m+10=0\Rightarrow\left[{}\begin{matrix}m=5\\m=-1\left(loại\right)\end{matrix}\right.\)