\(a,\Rightarrow27x^3+1-27x^3-27x=28\\ \Rightarrow-27x=27\\ \Rightarrow x=-1\\ b,\Rightarrow x^2\left(x-4\right)-9\left(x-4\right)=0\\ \Rightarrow\left(x-3\right)\left(x+3\right)\left(x-4\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=3\\x=4\\x=-3\end{matrix}\right.\\ c,\Rightarrow3x^2+6x-2x-4=0\\ \Rightarrow\left(x+2\right)\left(3x-2\right)=0\Rightarrow\left[{}\begin{matrix}x=\dfrac{2}{3}\\x=-2\end{matrix}\right.\)
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