\(a,\Leftrightarrow7x=\dfrac{7}{12}\Leftrightarrow x=\dfrac{1}{12}\\ b,\Leftrightarrow\left|\dfrac{1}{3}x-2\right|=\dfrac{1}{15}\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{3}x-2=\dfrac{1}{15}\\\dfrac{1}{3}x-2=-\dfrac{1}{15}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{3}x=\dfrac{31}{15}\\\dfrac{1}{3}x=\dfrac{29}{15}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{31}{5}\\x=\dfrac{29}{5}\end{matrix}\right.\\ c,\Leftrightarrow3^{x+1}\left(3+4\right)=7\cdot3^6\\ \Leftrightarrow3^{x+1}\cdot7=3^6\cdot7\\ \Leftrightarrow x+1=6\Leftrightarrow x=5\)
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