a) \(\left|x-\dfrac{2}{7}\right|-\dfrac{5}{6}=0\)
\(\left|x-\dfrac{2}{7}\right|=0+\dfrac{5}{6}=\dfrac{5}{6}\)
`=>`\(\left[{}\begin{matrix}x-\dfrac{2}{7}=\dfrac{5}{6}\\x-\dfrac{2}{7}=-\dfrac{5}{6}\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=\dfrac{47}{42}\\x=-\dfrac{23}{42}\end{matrix}\right.\)
b) \(3^x+3^{x+2}=810\)
`=>`\(\left(3^x\cdot1\right)+\left(3^x\cdot3^2\right)=810\)
\(3^x\cdot\left(1+3^2\right)=810\)
\(3^x\cdot\left(1+9\right)=810\)
\(3^x\cdot10=810\)
\(3^x=\dfrac{810}{10}\)
\(3^x=81\)
\(3^x=3^4\)
`=>x=4`
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