\(-2x^2+13x=23\)
\(\Leftrightarrow-2x^2+13x-23=0\)
\(\Leftrightarrow-2\left(x^2-\dfrac{13x}{2}+\dfrac{23}{2}\right)=0\)
\(\Leftrightarrow-2\left(x^2-\dfrac{13x}{2}+\dfrac{169}{16}+\dfrac{15}{16}\right)=0\)
\(\Leftrightarrow-2\left(x^2-\dfrac{13x}{2}+\dfrac{169}{16}\right)-\dfrac{15}{8}=0\)
\(\Leftrightarrow-2\left(x-\dfrac{13}{4}\right)^2-\dfrac{15}{8}=0\)
Dễ thấy: \(-2\left(x-\dfrac{13}{4}\right)^2-\dfrac{15}{8}\le-\dfrac{15}{8}< 0\)
Nên pt vô nghiệm
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