\(a,4.\left(x-5\right)-3.\left(x+7\right)=12\)
\(4x-20-3x-21=12\)
\(x-41=12\)
\(x=12+41\)
\(x=53\)
\(b,\left(x-4\right).\left(x-7\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x-4=0\\x-7=0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=4\\x=7\end{cases}}\)
a) \(4\left(x-5\right)-3.\left(x+7\right)=12\)
\(4x-4.5-3x+3.7=12\)
\(4x-20-3x+21=12\)
\(4x-3x=12+20-21\)
\(x=12+20-21\)
\(x=32-21\)
\(x=11\)
Vậy \(x=11\)