Tìm x biết: (2x-7)^3 - 27 = 0

* Hướng dẫn giải

Tìm x:

$\begin{array}{l}{\left(2\mathrm{x}-7\right)}^3-27=0\\ {\left(2\mathrm{x}-7\right)}^3-3^3=0\iff \left(2\mathrm{x}-10\right)\left(4{\mathrm{x}}^2-28\mathrm{x}+49+6\mathrm{x}+21+9\right)=0\\ \left(2\mathrm{x}-10\right)\left(4{\mathrm{x}}^2-22\mathrm{x}+79\right)=0\\ \mathrm{Do}4{\mathrm{x}}^2-22\mathrm{x}+79={\left(2\mathrm{x}-\frac{11}{2}\right)}^2+\frac{195}{4}>0\\ \Rightarrow 2\mathrm{x}-10=0\Rightarrow \mathrm{x}=5\end{array}$