\(4^x=t>0\Rightarrow f\left(t\right)=\left(m+1\right)t^2-2\left(2m-3\right)t+6m+5=0\) (1)
Pt có 2 nghiệm trái dấu khi (1) có 2 nghiệm thỏa mãn: \(0< t_1< 1< t_2\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(m+1\right).f\left(0\right)>0\\\left(m+1\right).f\left(1\right)< 0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(m+1\right)\left(6m+5\right)>0\\\left(m+1\right)\left(3m+12\right)< 0\end{matrix}\right.\)
\(\Rightarrow-4< m< -1\)
Đúng 2
Bình luận (7)
