a.
ĐKXĐ: \(x>0\)
\(logx=2\Rightarrow x=10^2=100\)
b.
ĐKXĐ: \(x>\dfrac{3}{2}\)
\(log_45x=log_4\left(2x-3\right)\Rightarrow5x=2x-3\)
\(\Rightarrow x=-1\) (ktm ĐKXĐ)
Vậy pt vô nghiệm
c.
ĐKXĐ: \(x>0\)
\(log7x=4\Rightarrow7x=10^4\)
\(\Rightarrow x=\dfrac{10^4}{7}\)
d.
ĐKXĐ: \(x>0\)
\(ln\left(x^2+5\right)=ln\left(6x\right)\Rightarrow x^2+5=6x\)
\(\Leftrightarrow x^2-6x+5=0\Rightarrow\left[{}\begin{matrix}x=1\\x=5\end{matrix}\right.\)