Lời giải:
\(-7x^2+3x+3=0\)
\(\Leftrightarrow 7x^2-3x-3=0\)
\(\Leftrightarrow 7(x^2-\frac{3}{7}x+\frac{3^2}{14^2})-\frac{93}{28}=0\)
\(\Leftrightarrow 7(x-\frac{3}{14})^2=\frac{93}{28}\)
\(\Leftrightarrow (x-\frac{3}{14})^2=\frac{93}{196}\Rightarrow \left[\begin{matrix} x-\frac{3}{14}=\frac{\sqrt{93}}{14}\\ x-\frac{3}{14}=-\frac{\sqrt{93}}{14}\end{matrix}\right.\Rightarrow \left[\begin{matrix} x=\frac{3}{14}+\frac{\sqrt{93}}{14}\\ x=\frac{3}{14}-\frac{\sqrt{93}}{14}\end{matrix}\right.\)
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